* same with xv6

[mascara-docs.git] / i386 / ucla / src / lab4 / kern / env.c

/* See COPYRIGHT for copyright information. */

#include <inc/x86.h>
#include <inc/mmu.h>
#include <inc/error.h>
#include <inc/string.h>
#include <inc/assert.h>
#include <inc/elf.h>

#include <kern/env.h>
#include <kern/pmap.h>
#include <kern/trap.h>
#include <kern/monitor.h>
#include <kern/sched.h>

struct Env *envs = NULL;                // All environments
struct Env *curenv = NULL;              // The current env
static Env *env_free_list = NULL;       // Free list

#define ENVGENSHIFT     12              // >= LOGNENV

//
// Converts an envid to an env pointer.
// If checkperm is set, the specified environment must be either the
// current environment or an immediate child of the current environment.
//
// RETURNS
//   0 on success, -E_BAD_ENV on error.
//   On success, sets *env_store to the environment.
//   On error, sets *env_store to NULL.
//
int
envid2env(envid_t envid, struct Env **env_store, bool checkperm)
{
        struct Env *e;

        // If envid is zero, return the current environment.
        if (envid == 0) {
                *env_store = curenv;
                return 0;
        }

        // Look up the Env structure via the index part of the envid,
        // then check the env_id field in that struct Env
        // to ensure that the envid is not stale
        // (i.e., does not refer to a _previous_ environment
        // that used the same slot in the envs[] array).
        e = &envs[ENVX(envid)];
        if (e->env_status == ENV_FREE || e->env_id != envid) {
                *env_store = 0;
                return -E_BAD_ENV;
        }

        // Check that the calling environment has legitimate permission
        // to manipulate the specified environment.
        // If checkperm is set, the specified environment
        // must be either the current environment
        // or an immediate child of the current environment.
        if (checkperm && e != curenv && e->env_parent_id != curenv->env_id) {
                *env_store = 0;
                return -E_BAD_ENV;
        }

        *env_store = e;
        return 0;
}

//
// Mark all environments in 'envs' as free, set their env_ids to 0,
// and insert them into the env_free_list.
// Insert in reverse order, so that the first call to env_alloc()
// returns envs[0].  (This is important for grading.)
//
void
env_init(void)
{
        // LAB 3: Your code here.
}

//
// Initialize the kernel virtual memory layout for environment e.
// Allocate a page directory, set e->env_pgdir accordingly,
// and initialize the kernel portion of the new environment's address space.
// Do NOT (yet) map anything into the user portion
// of the environment's virtual address space.
//
// Returns 0 on success, < 0 on error.  Errors include:
//      -E_NO_MEM if page directory or table could not be allocated.
//
static int
env_mem_init(struct Env *e)
{
        pte_t i;
        int r;
        struct Page *p;

        // Allocate a page for the page directory
        p = page_alloc();
        if (!p)
                return -E_NO_MEM;

        // Now, set e->env_pgdir and initialize the page directory.
        //
        // Hint:
        //    - Remember that page_alloc doesn't zero the page.
        //    - The VA space of all envs is identical above UTOP
        //      (except at UVPT, which we've set below).
        //      See inc/memlayout.h for permissions and layout.
        //      Can you use kern_pgdir as a template?  Hint: Yes.
        //      (Make sure you got the permissions right in Lab 2.)
        //    - The initial VA below UTOP is empty.
        //    - You do not need to make any more calls to page_alloc.
        //    - Note: In general, pp_ref is not maintained for
        //      physical pages mapped only above UTOP, but env_pgdir
        //      is an exception -- you need to increment env_pgdir's
        //      pp_ref for env_free to work correctly.
        //    - The functions in kern/pmap.h are handy.

        // LAB 3: Your code here.

        // UVPT maps the env's own page table read-only.
        // Permissions: kernel R, user R
        e->env_pgdir[PDX(UVPT)] = PADDR(e->env_pgdir) | PTE_P | PTE_U;

        return 0;
}

//
// Allocates and initializes a new environment.
// On success, the new environment is stored in *newenv_store.
//
// Returns 0 on success, < 0 on failure.  Errors include:
//      -E_NO_FREE_ENV if all NENVS environments are allocated
//      -E_NO_MEM on memory exhaustion
//
int
env_alloc(struct Env **newenv_store, envid_t parent_id)
{
        int32_t generation;
        int r;
        struct Env *e = env_free_list;
        if (!e)
                return -E_NO_FREE_ENV;

        // Allocate and set up the page directory for this environment.
        if ((r = env_mem_init(e)) < 0)
                return r;

        // Generate an env_id for this environment.
        generation = (e->env_id + (1 << ENVGENSHIFT)) & ~(NENV - 1);
        if (generation <= 0)    // Don't create a negative env_id.
                generation = 1 << ENVGENSHIFT;
        e->env_id = generation | (e - envs);

        // Set the basic status variables.
        e->env_parent_id = parent_id;
        e->env_status = ENV_RUNNABLE;
        e->env_runs = 0;

        // Clear out all the saved register state,
        // to prevent the register values
        // of a prior environment inhabiting this Env structure
        // from "leaking" into our new environment.
        memset(&e->env_tf, 0, sizeof(e->env_tf));

        // Set up appropriate initial values for the segment registers.
        // GD_UD is the user data segment selector in the GDT, and
        // GD_UT is the user text segment selector (see inc/memlayout.h).
        // The low 2 bits of each segment register contains the
        // Requestor Privilege Level (RPL); 3 means user mode.
        e->env_tf.tf_ds = GD_UD | 3;
        e->env_tf.tf_es = GD_UD | 3;
        e->env_tf.tf_ss = GD_UD | 3;
        e->env_tf.tf_esp = USTACKTOP;
        e->env_tf.tf_cs = GD_UT | 3;
        // You will set e->env_tf.tf_eip later.

        // Enable interrupts while in user mode.
        // LAB 4: Your code here.

        // Clear the page fault handler until user installs one.
        e->env_pgfault_upcall = 0;

        // Also clear the IPC receiving flag.
        e->env_ipc_recving = 0;

        // commit the allocation
        env_free_list = e->env_next;
        *newenv_store = e;

        cprintf("[%08x] new env %08x\n", curenv ? curenv->env_id : 0, e->env_id);
        return 0;
}

//
// Allocate at least len bytes of physical memory for environment env,
// and map it at virtual address va in the environment's address space.
// Does not zero or otherwise initialize the mapped pages in any way.
// Pages should be writable by user and kernel.
// Panic if any allocation attempt fails.
//
static void
segment_alloc(struct Env *e, uintptr_t va, size_t len)
{
        // LAB 3: Your code here.
        // (But only if you need it for load_elf.)
        //
        // Hint: It is easier to use segment_alloc if the caller can pass
        //   'va' and 'len' values that are not page-aligned.
        //   You should round 'va' down, and round 'va + len' up.
}

//
// Set up the initial program binary, stack, and processor flags
// for a user process.
//
// This function loads all loadable segments from the ELF binary image
// into the environment's user memory, starting at the appropriate
// virtual addresses indicated in the ELF program header.
// It also clears to zero any portions of these segments
// that are marked in the program header as being mapped
// but not actually present in the ELF file -- i.e., the program's bss section.
//
// Finally, this function maps one page for the program's initial stack.
//
// load_elf panics if it encounters problems.
//  - How might load_elf fail?  What might be wrong with the given input?
//
static void
load_elf(struct Env *e, uint8_t *binary, size_t size)
{
        struct Elf *elf = (struct Elf *) binary;
        // Load each program segment into environment 'e's virtual memory
        // at the address specified in the ELF section header.
        // Only load segments with ph->p_type == ELF_PROG_LOAD.
        // Each segment's virtual address can be found in ph->p_va
        // and its size in memory can be found in ph->p_memsz.
        // The ph->p_filesz bytes from the ELF binary, starting at
        // 'binary + ph->p_offset', should be copied to virtual address
        // ph->p_va.  Any remaining memory bytes should be cleared to zero.
        // (The ELF header should have ph->p_filesz <= ph->p_memsz.)
        // Use functions from the previous lab to allocate and map pages.
        //
        // All page protection bits should be user read/write for now.
        // ELF segments are not necessarily page-aligned, but you can
        // assume for this function that no two segments will touch
        // the same virtual page.
        //
        // You may find a function like segment_alloc useful.
        //
        // Loading the segments is much simpler if you can move data
        // directly into the virtual addresses stored in the ELF binary.
        // So which page directory should be in force during
        // this function?
        //
        // All this is very similar to what our boot loader does, except the
        // boot loader reads the code from disk and doesn't check whether
        // segments are loadable.  Take a look at boot/main.c to get ideas.
        //
        // You must also store the program's entry point somewhere,
        // to make sure that the environment starts executing at that point.
        // See env_run() and env_iret() below.

        // LAB 3: Your code here.


        // Now map one page for the program's initial stack
        // at virtual address USTACKTOP - PGSIZE.
        // (What should the permissions be?)

        // LAB 3: Your code here.
}

//
// Creates a new env running a specific binary.
// The new env's parent ID is set to 0.
// The implementation is a simple wrapper around env_alloc and load_elf.
//
void
env_create(uint8_t *binary, size_t size)
{
        // LAB 3: Your code here.
}

//
// Frees env e and all memory it uses.
//
void
env_free(struct Env *e)
{
        pde_t *pgdir;
        pte_t *pt;
        uint32_t pdeno, pteno;
        physaddr_t pa;

        // If freeing the current environment, switch to kern_pgdir
        // before freeing the page directory, just in case the page
        // gets reused.
        if (e == curenv)
                lcr3(PADDR(kern_pgdir));

        // Note the environment's demise.
        cprintf("[%08x] free env %08x\n", curenv ? curenv->env_id : 0, e->env_id);

        // Flush all mapped pages in the user portion of the address space
        static_assert(UTOP % PTSIZE == 0);
        pgdir = e->env_pgdir;
        for (pdeno = 0; pdeno < PDX(UTOP); pdeno++) {
                // only look at mapped page tables
                if (!(pgdir[pdeno] & PTE_P))
                        continue;

                // find the pa and va of the page table
                pt = (pte_t *) KADDR(PTE_ADDR(pgdir[pdeno]));

                // unmap all PTEs in this page table
                for (pteno = 0; pteno <= PTX(~0); pteno++) {
                        if (pt[pteno] & PTE_P)
                                page_remove(pgdir, PGADDR(pdeno, pteno, 0));
                }

                // free the page table itself
                pgdir[pdeno] = 0;
                page_decref(kva2page(pt));
        }

        // free the page directory
        e->env_pgdir = 0;
        page_decref(kva2page(pgdir));

        // return the environment to the free list
        e->env_status = ENV_FREE;
        e->env_next = env_free_list;
        env_free_list = e;
}

//
// Frees environment e.
// If e was the current env, then runs a new environment (and does not return
// to the caller).
//
void
env_destroy(struct Env *e)
{
        env_free(e);

        if (curenv == e) {
                curenv = NULL;
                sched_yield();
        }
}


//
// Restores the register values in the Trapframe with the 'iret' instruction.
// This exits the kernel and starts executing some environment's code
// at the location and registers specified in the Trapframe.
//
// This function does not return.
//
void
env_iret(struct Trapframe *tf)
{
        __asm __volatile("movl %0,%%esp\n"
                "\tpopal\n"
                "\tpopl %%es\n"
                "\tpopl %%ds\n"
                "\taddl $0x8,%%esp\n" /* skip tf_trapno and tf_errcode */
                "\tiret"
                : : "g" (tf) : "memory");
        panic("iret failed");  /* mostly to placate the compiler */
}

//
// Context switch from curenv to env e.
// Note: if this is the first call to env_run, curenv is NULL.
//
// This function does not return.
//
void
env_run(struct Env *e)
{
        // Step 1: If this is a context switch (a new environment is running),
        //         then set 'curenv' to the new environment,
        //         update its 'env_runs' counter, and
        //         and use lcr3() to switch to its address space.
        // Step 2: Use env_iret() to restore the environment's
        //         registers and drop into user mode in the
        //         environment.

        // Hint: This function loads the new environment's state from
        //      e->env_tf.  Go back through the code you wrote above
        //      and make sure you have set the relevant parts of
        //      e->env_tf to sensible values.

        // LAB 3: Your code here.

        panic("env_run not yet implemented");
}