mei: me: add cannon point device ids

[linux/fpc-iii.git] / drivers / iommu / intel-svm.c

/*
 * Copyright © 2015 Intel Corporation.
 *
 * This program is free software; you can redistribute it and/or modify it
 * under the terms and conditions of the GNU General Public License,
 * version 2, as published by the Free Software Foundation.
 *
 * This program is distributed in the hope it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License for
 * more details.
 *
 * Authors: David Woodhouse <dwmw2@infradead.org>
 */

#include <linux/intel-iommu.h>
#include <linux/mmu_notifier.h>
#include <linux/sched.h>
#include <linux/sched/mm.h>
#include <linux/slab.h>
#include <linux/intel-svm.h>
#include <linux/rculist.h>
#include <linux/pci.h>
#include <linux/pci-ats.h>
#include <linux/dmar.h>
#include <linux/interrupt.h>
#include <asm/page.h>

static irqreturn_t prq_event_thread(int irq, void *d);

struct pasid_entry {
        u64 val;
};

struct pasid_state_entry {
        u64 val;
};

int intel_svm_alloc_pasid_tables(struct intel_iommu *iommu)
{
        struct page *pages;
        int order;

        /* Start at 2 because it's defined as 2^(1+PSS) */
        iommu->pasid_max = 2 << ecap_pss(iommu->ecap);

        /* Eventually I'm promised we will get a multi-level PASID table
         * and it won't have to be physically contiguous. Until then,
         * limit the size because 8MiB contiguous allocations can be hard
         * to come by. The limit of 0x20000, which is 1MiB for each of
         * the PASID and PASID-state tables, is somewhat arbitrary. */
        if (iommu->pasid_max > 0x20000)
                iommu->pasid_max = 0x20000;

        order = get_order(sizeof(struct pasid_entry) * iommu->pasid_max);
        pages = alloc_pages(GFP_KERNEL | __GFP_ZERO, order);
        if (!pages) {
                pr_warn("IOMMU: %s: Failed to allocate PASID table\n",
                        iommu->name);
                return -ENOMEM;
        }
        iommu->pasid_table = page_address(pages);
        pr_info("%s: Allocated order %d PASID table.\n", iommu->name, order);

        if (ecap_dis(iommu->ecap)) {
                /* Just making it explicit... */
                BUILD_BUG_ON(sizeof(struct pasid_entry) != sizeof(struct pasid_state_entry));
                pages = alloc_pages(GFP_KERNEL | __GFP_ZERO, order);
                if (pages)
                        iommu->pasid_state_table = page_address(pages);
                else
                        pr_warn("IOMMU: %s: Failed to allocate PASID state table\n",
                                iommu->name);
        }

        idr_init(&iommu->pasid_idr);

        return 0;
}

int intel_svm_free_pasid_tables(struct intel_iommu *iommu)
{
        int order = get_order(sizeof(struct pasid_entry) * iommu->pasid_max);

        if (iommu->pasid_table) {
                free_pages((unsigned long)iommu->pasid_table, order);
                iommu->pasid_table = NULL;
        }
        if (iommu->pasid_state_table) {
                free_pages((unsigned long)iommu->pasid_state_table, order);
                iommu->pasid_state_table = NULL;
        }
        idr_destroy(&iommu->pasid_idr);
        return 0;
}

#define PRQ_ORDER 0

int intel_svm_enable_prq(struct intel_iommu *iommu)
{
        struct page *pages;
        int irq, ret;

        pages = alloc_pages(GFP_KERNEL | __GFP_ZERO, PRQ_ORDER);
        if (!pages) {
                pr_warn("IOMMU: %s: Failed to allocate page request queue\n",
                        iommu->name);
                return -ENOMEM;
        }
        iommu->prq = page_address(pages);

        irq = dmar_alloc_hwirq(DMAR_UNITS_SUPPORTED + iommu->seq_id, iommu->node, iommu);
        if (irq <= 0) {
                pr_err("IOMMU: %s: Failed to create IRQ vector for page request queue\n",
                       iommu->name);
                ret = -EINVAL;
        err:
                free_pages((unsigned long)iommu->prq, PRQ_ORDER);
                iommu->prq = NULL;
                return ret;
        }
        iommu->pr_irq = irq;

        snprintf(iommu->prq_name, sizeof(iommu->prq_name), "dmar%d-prq", iommu->seq_id);

        ret = request_threaded_irq(irq, NULL, prq_event_thread, IRQF_ONESHOT,
                                   iommu->prq_name, iommu);
        if (ret) {
                pr_err("IOMMU: %s: Failed to request IRQ for page request queue\n",
                       iommu->name);
                dmar_free_hwirq(irq);
                goto err;
        }
        dmar_writeq(iommu->reg + DMAR_PQH_REG, 0ULL);
        dmar_writeq(iommu->reg + DMAR_PQT_REG, 0ULL);
        dmar_writeq(iommu->reg + DMAR_PQA_REG, virt_to_phys(iommu->prq) | PRQ_ORDER);

        return 0;
}

int intel_svm_finish_prq(struct intel_iommu *iommu)
{
        dmar_writeq(iommu->reg + DMAR_PQH_REG, 0ULL);
        dmar_writeq(iommu->reg + DMAR_PQT_REG, 0ULL);
        dmar_writeq(iommu->reg + DMAR_PQA_REG, 0ULL);

        free_irq(iommu->pr_irq, iommu);
        dmar_free_hwirq(iommu->pr_irq);
        iommu->pr_irq = 0;

        free_pages((unsigned long)iommu->prq, PRQ_ORDER);
        iommu->prq = NULL;

        return 0;
}

static void intel_flush_svm_range_dev (struct intel_svm *svm, struct intel_svm_dev *sdev,
                                       unsigned long address, unsigned long pages, int ih, int gl)
{
        struct qi_desc desc;

        if (pages == -1) {
                /* For global kernel pages we have to flush them in *all* PASIDs
                 * because that's the only option the hardware gives us. Despite
                 * the fact that they are actually only accessible through one. */
                if (gl)
                        desc.low = QI_EIOTLB_PASID(svm->pasid) | QI_EIOTLB_DID(sdev->did) |
                                QI_EIOTLB_GRAN(QI_GRAN_ALL_ALL) | QI_EIOTLB_TYPE;
                else
                        desc.low = QI_EIOTLB_PASID(svm->pasid) | QI_EIOTLB_DID(sdev->did) |
                                QI_EIOTLB_GRAN(QI_GRAN_NONG_PASID) | QI_EIOTLB_TYPE;
                desc.high = 0;
        } else {
                int mask = ilog2(__roundup_pow_of_two(pages));

                desc.low = QI_EIOTLB_PASID(svm->pasid) | QI_EIOTLB_DID(sdev->did) |
                        QI_EIOTLB_GRAN(QI_GRAN_PSI_PASID) | QI_EIOTLB_TYPE;
                desc.high = QI_EIOTLB_ADDR(address) | QI_EIOTLB_GL(gl) |
                        QI_EIOTLB_IH(ih) | QI_EIOTLB_AM(mask);
        }
        qi_submit_sync(&desc, svm->iommu);

        if (sdev->dev_iotlb) {
                desc.low = QI_DEV_EIOTLB_PASID(svm->pasid) | QI_DEV_EIOTLB_SID(sdev->sid) |
                        QI_DEV_EIOTLB_QDEP(sdev->qdep) | QI_DEIOTLB_TYPE;
                if (pages == -1) {
                        desc.high = QI_DEV_EIOTLB_ADDR(-1ULL >> 1) | QI_DEV_EIOTLB_SIZE;
                } else if (pages > 1) {
                        /* The least significant zero bit indicates the size. So,
                         * for example, an "address" value of 0x12345f000 will
                         * flush from 0x123440000 to 0x12347ffff (256KiB). */
                        unsigned long last = address + ((unsigned long)(pages - 1) << VTD_PAGE_SHIFT);
                        unsigned long mask = __rounddown_pow_of_two(address ^ last);;

                        desc.high = QI_DEV_EIOTLB_ADDR((address & ~mask) | (mask - 1)) | QI_DEV_EIOTLB_SIZE;
                } else {
                        desc.high = QI_DEV_EIOTLB_ADDR(address);
                }
                qi_submit_sync(&desc, svm->iommu);
        }
}

static void intel_flush_svm_range(struct intel_svm *svm, unsigned long address,
                                  unsigned long pages, int ih, int gl)
{
        struct intel_svm_dev *sdev;

        /* Try deferred invalidate if available */
        if (svm->iommu->pasid_state_table &&
            !cmpxchg64(&svm->iommu->pasid_state_table[svm->pasid].val, 0, 1ULL << 63))
                return;

        rcu_read_lock();
        list_for_each_entry_rcu(sdev, &svm->devs, list)
                intel_flush_svm_range_dev(svm, sdev, address, pages, ih, gl);
        rcu_read_unlock();
}

static void intel_change_pte(struct mmu_notifier *mn, struct mm_struct *mm,
                             unsigned long address, pte_t pte)
{
        struct intel_svm *svm = container_of(mn, struct intel_svm, notifier);

        intel_flush_svm_range(svm, address, 1, 1, 0);
}

/* Pages have been freed at this point */
static void intel_invalidate_range(struct mmu_notifier *mn,
                                   struct mm_struct *mm,
                                   unsigned long start, unsigned long end)
{
        struct intel_svm *svm = container_of(mn, struct intel_svm, notifier);

        intel_flush_svm_range(svm, start,
                              (end - start + PAGE_SIZE - 1) >> VTD_PAGE_SHIFT, 0, 0);
}


static void intel_flush_pasid_dev(struct intel_svm *svm, struct intel_svm_dev *sdev, int pasid)
{
        struct qi_desc desc;

        desc.high = 0;
        desc.low = QI_PC_TYPE | QI_PC_DID(sdev->did) | QI_PC_PASID_SEL | QI_PC_PASID(pasid);

        qi_submit_sync(&desc, svm->iommu);
}

static void intel_mm_release(struct mmu_notifier *mn, struct mm_struct *mm)
{
        struct intel_svm *svm = container_of(mn, struct intel_svm, notifier);
        struct intel_svm_dev *sdev;

        /* This might end up being called from exit_mmap(), *before* the page
         * tables are cleared. And __mmu_notifier_release() will delete us from
         * the list of notifiers so that our invalidate_range() callback doesn't
         * get called when the page tables are cleared. So we need to protect
         * against hardware accessing those page tables.
         *
         * We do it by clearing the entry in the PASID table and then flushing
         * the IOTLB and the PASID table caches. This might upset hardware;
         * perhaps we'll want to point the PASID to a dummy PGD (like the zero
         * page) so that we end up taking a fault that the hardware really
         * *has* to handle gracefully without affecting other processes.
         */
        svm->iommu->pasid_table[svm->pasid].val = 0;
        wmb();

        rcu_read_lock();
        list_for_each_entry_rcu(sdev, &svm->devs, list) {
                intel_flush_pasid_dev(svm, sdev, svm->pasid);
                intel_flush_svm_range_dev(svm, sdev, 0, -1, 0, !svm->mm);
        }
        rcu_read_unlock();

}

static const struct mmu_notifier_ops intel_mmuops = {
        .release = intel_mm_release,
        .change_pte = intel_change_pte,
        .invalidate_range = intel_invalidate_range,
};

static DEFINE_MUTEX(pasid_mutex);

int intel_svm_bind_mm(struct device *dev, int *pasid, int flags, struct svm_dev_ops *ops)
{
        struct intel_iommu *iommu = intel_svm_device_to_iommu(dev);
        struct intel_svm_dev *sdev;
        struct intel_svm *svm = NULL;
        struct mm_struct *mm = NULL;
        int pasid_max;
        int ret;

        if (WARN_ON(!iommu || !iommu->pasid_table))
                return -EINVAL;

        if (dev_is_pci(dev)) {
                pasid_max = pci_max_pasids(to_pci_dev(dev));
                if (pasid_max < 0)
                        return -EINVAL;
        } else
                pasid_max = 1 << 20;

        if ((flags & SVM_FLAG_SUPERVISOR_MODE)) {
                if (!ecap_srs(iommu->ecap))
                        return -EINVAL;
        } else if (pasid) {
                mm = get_task_mm(current);
                BUG_ON(!mm);
        }

        mutex_lock(&pasid_mutex);
        if (pasid && !(flags & SVM_FLAG_PRIVATE_PASID)) {
                int i;

                idr_for_each_entry(&iommu->pasid_idr, svm, i) {
                        if (svm->mm != mm ||
                            (svm->flags & SVM_FLAG_PRIVATE_PASID))
                                continue;

                        if (svm->pasid >= pasid_max) {
                                dev_warn(dev,
                                         "Limited PASID width. Cannot use existing PASID %d\n",
                                         svm->pasid);
                                ret = -ENOSPC;
                                goto out;
                        }

                        list_for_each_entry(sdev, &svm->devs, list) {
                                if (dev == sdev->dev) {
                                        if (sdev->ops != ops) {
                                                ret = -EBUSY;
                                                goto out;
                                        }
                                        sdev->users++;
                                        goto success;
                                }
                        }

                        break;
                }
        }

        sdev = kzalloc(sizeof(*sdev), GFP_KERNEL);
        if (!sdev) {
                ret = -ENOMEM;
                goto out;
        }
        sdev->dev = dev;

        ret = intel_iommu_enable_pasid(iommu, sdev);
        if (ret || !pasid) {
                /* If they don't actually want to assign a PASID, this is
                 * just an enabling check/preparation. */
                kfree(sdev);
                goto out;
        }
        /* Finish the setup now we know we're keeping it */
        sdev->users = 1;
        sdev->ops = ops;
        init_rcu_head(&sdev->rcu);

        if (!svm) {
                svm = kzalloc(sizeof(*svm), GFP_KERNEL);
                if (!svm) {
                        ret = -ENOMEM;
                        kfree(sdev);
                        goto out;
                }
                svm->iommu = iommu;

                if (pasid_max > iommu->pasid_max)
                        pasid_max = iommu->pasid_max;

                /* Do not use PASID 0 in caching mode (virtualised IOMMU) */
                ret = idr_alloc(&iommu->pasid_idr, svm,
                                !!cap_caching_mode(iommu->cap),
                                pasid_max - 1, GFP_KERNEL);
                if (ret < 0) {
                        kfree(svm);
                        goto out;
                }
                svm->pasid = ret;
                svm->notifier.ops = &intel_mmuops;
                svm->mm = mm;
                svm->flags = flags;
                INIT_LIST_HEAD_RCU(&svm->devs);
                ret = -ENOMEM;
                if (mm) {
                        ret = mmu_notifier_register(&svm->notifier, mm);
                        if (ret) {
                                idr_remove(&svm->iommu->pasid_idr, svm->pasid);
                                kfree(svm);
                                kfree(sdev);
                                goto out;
                        }
                        iommu->pasid_table[svm->pasid].val = (u64)__pa(mm->pgd) | 1;
                } else
                        iommu->pasid_table[svm->pasid].val = (u64)__pa(init_mm.pgd) | 1 | (1ULL << 11);
                wmb();
                /* In caching mode, we still have to flush with PASID 0 when
                 * a PASID table entry becomes present. Not entirely clear
                 * *why* that would be the case — surely we could just issue
                 * a flush with the PASID value that we've changed? The PASID
                 * is the index into the table, after all. It's not like domain
                 * IDs in the case of the equivalent context-entry change in
                 * caching mode. And for that matter it's not entirely clear why
                 * a VMM would be in the business of caching the PASID table
                 * anyway. Surely that can be left entirely to the guest? */
                if (cap_caching_mode(iommu->cap))
                        intel_flush_pasid_dev(svm, sdev, 0);
        }
        list_add_rcu(&sdev->list, &svm->devs);

 success:
        *pasid = svm->pasid;
        ret = 0;
 out:
        mutex_unlock(&pasid_mutex);
        if (mm)
                mmput(mm);
        return ret;
}
EXPORT_SYMBOL_GPL(intel_svm_bind_mm);

int intel_svm_unbind_mm(struct device *dev, int pasid)
{
        struct intel_svm_dev *sdev;
        struct intel_iommu *iommu;
        struct intel_svm *svm;
        int ret = -EINVAL;

        mutex_lock(&pasid_mutex);
        iommu = intel_svm_device_to_iommu(dev);
        if (!iommu || !iommu->pasid_table)
                goto out;

        svm = idr_find(&iommu->pasid_idr, pasid);
        if (!svm)
                goto out;

        list_for_each_entry(sdev, &svm->devs, list) {
                if (dev == sdev->dev) {
                        ret = 0;
                        sdev->users--;
                        if (!sdev->users) {
                                list_del_rcu(&sdev->list);
                                /* Flush the PASID cache and IOTLB for this device.
                                 * Note that we do depend on the hardware *not* using
                                 * the PASID any more. Just as we depend on other
                                 * devices never using PASIDs that they have no right
                                 * to use. We have a *shared* PASID table, because it's
                                 * large and has to be physically contiguous. So it's
                                 * hard to be as defensive as we might like. */
                                intel_flush_pasid_dev(svm, sdev, svm->pasid);
                                intel_flush_svm_range_dev(svm, sdev, 0, -1, 0, !svm->mm);
                                kfree_rcu(sdev, rcu);

                                if (list_empty(&svm->devs)) {
                                        svm->iommu->pasid_table[svm->pasid].val = 0;
                                        wmb();

                                        idr_remove(&svm->iommu->pasid_idr, svm->pasid);
                                        if (svm->mm)
                                                mmu_notifier_unregister(&svm->notifier, svm->mm);

                                        /* We mandate that no page faults may be outstanding
                                         * for the PASID when intel_svm_unbind_mm() is called.
                                         * If that is not obeyed, subtle errors will happen.
                                         * Let's make them less subtle... */
                                        memset(svm, 0x6b, sizeof(*svm));
                                        kfree(svm);
                                }
                        }
                        break;
                }
        }
 out:
        mutex_unlock(&pasid_mutex);

        return ret;
}
EXPORT_SYMBOL_GPL(intel_svm_unbind_mm);

int intel_svm_is_pasid_valid(struct device *dev, int pasid)
{
        struct intel_iommu *iommu;
        struct intel_svm *svm;
        int ret = -EINVAL;

        mutex_lock(&pasid_mutex);
        iommu = intel_svm_device_to_iommu(dev);
        if (!iommu || !iommu->pasid_table)
                goto out;

        svm = idr_find(&iommu->pasid_idr, pasid);
        if (!svm)
                goto out;

        /* init_mm is used in this case */
        if (!svm->mm)
                ret = 1;
        else if (atomic_read(&svm->mm->mm_users) > 0)
                ret = 1;
        else
                ret = 0;

 out:
        mutex_unlock(&pasid_mutex);

        return ret;
}
EXPORT_SYMBOL_GPL(intel_svm_is_pasid_valid);

/* Page request queue descriptor */
struct page_req_dsc {
        u64 srr:1;
        u64 bof:1;
        u64 pasid_present:1;
        u64 lpig:1;
        u64 pasid:20;
        u64 bus:8;
        u64 private:23;
        u64 prg_index:9;
        u64 rd_req:1;
        u64 wr_req:1;
        u64 exe_req:1;
        u64 priv_req:1;
        u64 devfn:8;
        u64 addr:52;
};

#define PRQ_RING_MASK ((0x1000 << PRQ_ORDER) - 0x10)

static bool access_error(struct vm_area_struct *vma, struct page_req_dsc *req)
{
        unsigned long requested = 0;

        if (req->exe_req)
                requested |= VM_EXEC;

        if (req->rd_req)
                requested |= VM_READ;

        if (req->wr_req)
                requested |= VM_WRITE;

        return (requested & ~vma->vm_flags) != 0;
}

static bool is_canonical_address(u64 addr)
{
        int shift = 64 - (__VIRTUAL_MASK_SHIFT + 1);
        long saddr = (long) addr;

        return (((saddr << shift) >> shift) == saddr);
}

static irqreturn_t prq_event_thread(int irq, void *d)
{
        struct intel_iommu *iommu = d;
        struct intel_svm *svm = NULL;
        int head, tail, handled = 0;

        /* Clear PPR bit before reading head/tail registers, to
         * ensure that we get a new interrupt if needed. */
        writel(DMA_PRS_PPR, iommu->reg + DMAR_PRS_REG);

        tail = dmar_readq(iommu->reg + DMAR_PQT_REG) & PRQ_RING_MASK;
        head = dmar_readq(iommu->reg + DMAR_PQH_REG) & PRQ_RING_MASK;
        while (head != tail) {
                struct intel_svm_dev *sdev;
                struct vm_area_struct *vma;
                struct page_req_dsc *req;
                struct qi_desc resp;
                int ret, result;
                u64 address;

                handled = 1;

                req = &iommu->prq[head / sizeof(*req)];

                result = QI_RESP_FAILURE;
                address = (u64)req->addr << VTD_PAGE_SHIFT;
                if (!req->pasid_present) {
                        pr_err("%s: Page request without PASID: %08llx %08llx\n",
                               iommu->name, ((unsigned long long *)req)[0],
                               ((unsigned long long *)req)[1]);
                        goto bad_req;
                }

                if (!svm || svm->pasid != req->pasid) {
                        rcu_read_lock();
                        svm = idr_find(&iommu->pasid_idr, req->pasid);
                        /* It *can't* go away, because the driver is not permitted
                         * to unbind the mm while any page faults are outstanding.
                         * So we only need RCU to protect the internal idr code. */
                        rcu_read_unlock();

                        if (!svm) {
                                pr_err("%s: Page request for invalid PASID %d: %08llx %08llx\n",
                                       iommu->name, req->pasid, ((unsigned long long *)req)[0],
                                       ((unsigned long long *)req)[1]);
                                goto no_pasid;
                        }
                }

                result = QI_RESP_INVALID;
                /* Since we're using init_mm.pgd directly, we should never take
                 * any faults on kernel addresses. */
                if (!svm->mm)
                        goto bad_req;
                /* If the mm is already defunct, don't handle faults. */
                if (!mmget_not_zero(svm->mm))
                        goto bad_req;

                /* If address is not canonical, return invalid response */
                if (!is_canonical_address(address))
                        goto bad_req;

                down_read(&svm->mm->mmap_sem);
                vma = find_extend_vma(svm->mm, address);
                if (!vma || address < vma->vm_start)
                        goto invalid;

                if (access_error(vma, req))
                        goto invalid;

                ret = handle_mm_fault(vma, address,
                                      req->wr_req ? FAULT_FLAG_WRITE : 0);
                if (ret & VM_FAULT_ERROR)
                        goto invalid;

                result = QI_RESP_SUCCESS;
        invalid:
                up_read(&svm->mm->mmap_sem);
                mmput(svm->mm);
        bad_req:
                /* Accounting for major/minor faults? */
                rcu_read_lock();
                list_for_each_entry_rcu(sdev, &svm->devs, list) {
                        if (sdev->sid == PCI_DEVID(req->bus, req->devfn))
                                break;
                }
                /* Other devices can go away, but the drivers are not permitted
                 * to unbind while any page faults might be in flight. So it's
                 * OK to drop the 'lock' here now we have it. */
                rcu_read_unlock();

                if (WARN_ON(&sdev->list == &svm->devs))
                        sdev = NULL;

                if (sdev && sdev->ops && sdev->ops->fault_cb) {
                        int rwxp = (req->rd_req << 3) | (req->wr_req << 2) |
                                (req->exe_req << 1) | (req->priv_req);
                        sdev->ops->fault_cb(sdev->dev, req->pasid, req->addr, req->private, rwxp, result);
                }
                /* We get here in the error case where the PASID lookup failed,
                   and these can be NULL. Do not use them below this point! */
                sdev = NULL;
                svm = NULL;
        no_pasid:
                if (req->lpig) {
                        /* Page Group Response */
                        resp.low = QI_PGRP_PASID(req->pasid) |
                                QI_PGRP_DID((req->bus << 8) | req->devfn) |
                                QI_PGRP_PASID_P(req->pasid_present) |
                                QI_PGRP_RESP_TYPE;
                        resp.high = QI_PGRP_IDX(req->prg_index) |
                                QI_PGRP_PRIV(req->private) | QI_PGRP_RESP_CODE(result);

                        qi_submit_sync(&resp, iommu);
                } else if (req->srr) {
                        /* Page Stream Response */
                        resp.low = QI_PSTRM_IDX(req->prg_index) |
                                QI_PSTRM_PRIV(req->private) | QI_PSTRM_BUS(req->bus) |
                                QI_PSTRM_PASID(req->pasid) | QI_PSTRM_RESP_TYPE;
                        resp.high = QI_PSTRM_ADDR(address) | QI_PSTRM_DEVFN(req->devfn) |
                                QI_PSTRM_RESP_CODE(result);

                        qi_submit_sync(&resp, iommu);
                }

                head = (head + sizeof(*req)) & PRQ_RING_MASK;
        }

        dmar_writeq(iommu->reg + DMAR_PQH_REG, tail);

        return IRQ_RETVAL(handled);
}