Re: [PATCH 06/10] Introduce functions to dump mm

[Louis Rilling <Louis.Rilling@kerlabs.com>]

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On Sat, Oct 18, 2008 at 03:11:34AM +0400, Andrey Mirkin wrote:
> Functions to dump mm struct, VMAs and mm context are added.

Again, a few little comments.

[...]

> diff --git a/checkpoint/cpt_mm.c b/checkpoint/cpt_mm.c
> new file mode 100644
> index 0000000..8a22c48
> --- /dev/null
> +++ b/checkpoint/cpt_mm.c
> @@ -0,0 +1,434 @@
> +/*
> + *  Copyright (C) 2008 Parallels, Inc.
> + *
> + *  Authors:	Andrey Mirkin <major@openvz.org>
> + *
> + *  This program is free software; you can redistribute it and/or
> + *  modify it under the terms of the GNU General Public License as
> + *  published by the Free Software Foundation, version 2 of the
> + *  License.
> + *
> + */
> +
> +#include <linux/sched.h>
> +#include <linux/slab.h>
> +#include <linux/file.h>
> +#include <linux/mm.h>
> +#include <linux/errno.h>
> +#include <linux/major.h>
> +#include <linux/mman.h>
> +#include <linux/mnt_namespace.h>
> +#include <linux/mount.h>
> +#include <linux/namei.h>
> +#include <linux/pagemap.h>
> +#include <linux/hugetlb.h>
> +#include <asm/ldt.h>
> +
> +#include "checkpoint.h"
> +#include "cpt_image.h"
> +
> +struct page_area
> +{
> +	int type;
> +	unsigned long start;
> +	unsigned long end;
> +	pgoff_t pgoff;
> +	loff_t mm;
> +	__u64 list[16];
> +};
> +
> +struct page_desc
> +{
> +	int	type;
> +	pgoff_t	index;
> +	loff_t	mm;
> +	int	shared;
> +};
> +
> +enum {
> +	PD_ABSENT,
> +	PD_COPY,
> +	PD_FUNKEY,
> +};
> +
> +/* 0: page can be obtained from backstore, or still not mapped anonymous  page,
> +      or something else, which does not requre copy.
> +   1: page requires copy
> +   2: page requres copy but its content is zero. Quite useless.
> +   3: wp page is shared after fork(). It is to be COWed when modified.
> +   4: page is something unsupported... We copy it right now.
> + */
> +
> +static void page_get_desc(struct vm_area_struct *vma, unsigned long addr,
> +			  struct page_desc *pdesc, cpt_context_t * ctx)
> +{
> +	struct mm_struct *mm = vma->vm_mm;
> +	pgd_t *pgd;
> +	pud_t *pud;
> +	pmd_t *pmd;
> +	pte_t *ptep, pte;
> +	spinlock_t *ptl;
> +	struct page *pg = NULL;
> +	pgoff_t linear_index = (addr - vma->vm_start)/PAGE_SIZE + vma->vm_pgoff;
> +
> +	pdesc->index = linear_index;
> +	pdesc->shared = 0;
> +	pdesc->mm = CPT_NULL;
> +
> +	if (vma->vm_flags & VM_IO) {
> +		pdesc->type = PD_ABSENT;
> +		return;
> +	}
> +
> +	pgd = pgd_offset(mm, addr);
> +	if (pgd_none(*pgd) || unlikely(pgd_bad(*pgd)))
> +		goto out_absent;
> +	pud = pud_offset(pgd, addr);
> +	if (pud_none(*pud) || unlikely(pud_bad(*pud)))
> +		goto out_absent;
> +	pmd = pmd_offset(pud, addr);
> +	if (pmd_none(*pmd) || unlikely(pmd_bad(*pmd)))
> +		goto out_absent;
> +#ifdef CONFIG_X86
> +	if (pmd_huge(*pmd)) {
> +		eprintk("page_huge\n");
> +		goto out_unsupported;
> +	}
> +#endif
> +	ptep = pte_offset_map_lock(mm, pmd, addr, &ptl);
> +	pte = *ptep;
> +	pte_unmap(ptep);
> +
> +	if (pte_none(pte))
> +		goto out_absent_unlock;
> +
> +	if ((pg = vm_normal_page(vma, addr, pte)) == NULL) {
> +		pdesc->type = PD_COPY;
> +		goto out_unlock;
> +	}
> +
> +	get_page(pg);
> +	spin_unlock(ptl);
> +
> +	if (pg->mapping && !PageAnon(pg)) {
> +		if (vma->vm_file == NULL) {
> +			eprintk("pg->mapping!=NULL for fileless vma: %08lx\n", addr);
> +			goto out_unsupported;
> +		}
> +		if (vma->vm_file->f_mapping != pg->mapping) {
> +			eprintk("pg->mapping!=f_mapping: %08lx %p %p\n",
> +				    addr, vma->vm_file->f_mapping, pg->mapping);
> +			goto out_unsupported;
> +		}
> +		pdesc->index = (pg->index << (PAGE_CACHE_SHIFT - PAGE_SHIFT));
> +		/* Page is in backstore. For us it is like
> +		 * it is not present.
> +		 */
> +		goto out_absent;
> +	}
> +
> +	if (PageReserved(pg)) {
> +		/* Special case: ZERO_PAGE is used, when an
> +		 * anonymous page is accessed but not written. */
> +		if (pg == ZERO_PAGE(addr)) {
> +			if (pte_write(pte)) {
> +				eprintk("not funny already, writable ZERO_PAGE\n");
> +				goto out_unsupported;
> +			}
> +			/* Just copy it for now */
> +			pdesc->type = PD_COPY;
> +			goto out_put;
> +		}
> +		eprintk("reserved page %lu at %08lx\n", pg->index, addr);
> +		goto out_unsupported;
> +	}
> +
> +	if (!pg->mapping) {
> +		eprintk("page without mapping at %08lx\n", addr);
> +		goto out_unsupported;
> +	}
> +
> +	pdesc->type = PD_COPY;
> +
> +out_put:
> +	if (pg)
> +		put_page(pg);
> +	return;
> +
> +out_unlock:
> +	spin_unlock(ptl);
> +	goto out_put;
> +
> +out_absent_unlock:
> +	spin_unlock(ptl);
> +
> +out_absent:
> +	pdesc->type = PD_ABSENT;
> +	goto out_put;
> +
> +out_unsupported:
> +	pdesc->type = PD_FUNKEY;
> +	goto out_put;
> +}
> +
> +static int count_vma_pages(struct vm_area_struct *vma, struct cpt_context *ctx)
> +{
> +	unsigned long addr;
> +	int page_num = 0;
> +
> +	for (addr = vma->vm_start; addr < vma->vm_end; addr += PAGE_SIZE) {
> +		struct page_desc pd;
> +
> +		page_get_desc(vma, addr, &pd, ctx);
> +
> +		if (pd.type != PD_COPY) {
> +			return -EINVAL;
> +		} else {
> +			page_num += 1;
> +		}
> +		
> +	}
> +	return page_num;
> +}
> +
> +/* ATTN: We give "current" to get_user_pages(). This is wrong, but get_user_pages()
> + * does not really need this thing. It just stores some page fault stats there.
> + *
> + * BUG: some archs (f.e. sparc64, but not Intel*) require flush cache pages
> + * before accessing vma.
> + */
> +static int dump_pages(struct vm_area_struct *vma, unsigned long start,
> +		unsigned long end, struct cpt_context *ctx)
> +{
> +#define MAX_PAGE_BATCH 16
> +	struct page *pg[MAX_PAGE_BATCH];
> +	int npages = (end - start)/PAGE_SIZE;
> +	int count = 0;
> +
> +	while (count < npages) {
> +		int copy = npages - count;
> +		int n;
> +
> +		if (copy > MAX_PAGE_BATCH)
> +			copy = MAX_PAGE_BATCH;
> +		n = get_user_pages(current, vma->vm_mm, start, copy,
> +				   0, 1, pg, NULL);
> +		if (n == copy) {
> +			int i;
> +			for (i=0; i<n; i++) {
> +				char *maddr = kmap(pg[i]);
> +				ctx->write(maddr, PAGE_SIZE, ctx);
> +				kunmap(pg[i]);

There is no error handling in this inner loop. Should be fixed imho.

> +			}
> +		} else {
> +			eprintk("get_user_pages fault");
> +			for ( ; n > 0; n--)
> +				page_cache_release(pg[n-1]);
> +			return -EFAULT;
> +		}
> +		start += n*PAGE_SIZE;
> +		count += n;
> +		for ( ; n > 0; n--)
> +			page_cache_release(pg[n-1]);
> +	}
> +	return 0;
> +}
> +
> +static int dump_page_block(struct vm_area_struct *vma,
> +			   struct cpt_page_block *pgb,
> +			   struct cpt_context *ctx)
> +{
> +	int err;
> +	pgb->cpt_len = sizeof(*pgb) + pgb->cpt_end - pgb->cpt_start;
> +	pgb->cpt_type = CPT_OBJ_PAGES;
> +	pgb->cpt_hdrlen = sizeof(*pgb);
> +	pgb->cpt_content = CPT_CONTENT_DATA;
> +
> +	err = ctx->write(pgb, sizeof(*pgb), ctx);
> +	if (!err)
> +		err = dump_pages(vma, pgb->cpt_start, pgb->cpt_end, ctx);
> +
> +	return err;
> +}
> +
> +static int cpt_dump_dentry(struct path *p, cpt_context_t *ctx)
> +{
> +	int len;
> +	char *path;
> +	char *buf;
> +	struct cpt_object_hdr o;
> +
> +	buf = (char *)__get_free_page(GFP_KERNEL);
> +	if (!buf)
> +		return -ENOMEM;
> +
> +	path = d_path(p, buf, PAGE_SIZE);
> +
> +	if (IS_ERR(path)) {
> +		free_page((unsigned long)buf);
> +		return PTR_ERR(path);
> +	}
> +
> +	len = buf + PAGE_SIZE - 1 - path;
> +	o.cpt_len = sizeof(o) + len + 1;
> +	o.cpt_type = CPT_OBJ_NAME;
> +	o.cpt_hdrlen = sizeof(o);
> +	o.cpt_content = CPT_CONTENT_NAME;
> +	path[len] = 0;
> +
> +	ctx->write(&o, sizeof(o), ctx);
> +	ctx->write(path, len + 1, ctx);

Error handling?

> +	free_page((unsigned long)buf);
> +
> +	return 0;
> +}
> +
> +static int dump_one_vma(struct mm_struct *mm,
> +			struct vm_area_struct *vma, struct cpt_context *ctx)
> +{
> +	struct cpt_vma_image *v;
> +	unsigned long addr;
> +	int page_num;
> +	int err;
> +
> +	v = kzalloc(sizeof(*v), GFP_KERNEL);
> +	if (!v)
> +		return -ENOMEM;
> +
> +	v->cpt_len = sizeof(*v);
> +	v->cpt_type = CPT_OBJ_VMA;
> +	v->cpt_hdrlen = sizeof(*v);
> +	v->cpt_content = CPT_CONTENT_ARRAY;
> +
> +	v->cpt_start = vma->vm_start;
> +	v->cpt_end = vma->vm_end;
> +	v->cpt_flags = vma->vm_flags;
> +	if (vma->vm_flags & VM_HUGETLB) {
> +		eprintk("huge TLB VMAs are still not supported\n");
> +		kfree(v);
> +		return -EINVAL;
> +	}
> +	v->cpt_pgprot = vma->vm_page_prot.pgprot;
> +	v->cpt_pgoff = vma->vm_pgoff;
> +	v->cpt_file = CPT_NULL;
> +	v->cpt_vma_type = CPT_VMA_TYPE_0;
> +
> +	page_num = count_vma_pages(vma, ctx);
> +	if (page_num < 0) {
> +		kfree(v);
> +		return -EINVAL;
> +	}

AFAICS, since count_vma_pages only supports pages with PD_COPY, and since
get_page_desc() tags text segment pages (file-mapped and not anonymous since
not written to) as PD_ABSENT, no executable is checkpointable. So, where is the
trick? Am I completely missing something about page mapping?

> +	v->cpt_page_num = page_num;
> +
> +	if (vma->vm_file) {
> +		v->cpt_file = 0;
> +		v->cpt_vma_type = CPT_VMA_FILE;
> +	}
> +
> +	ctx->write(v, sizeof(*v), ctx);

Error handling?

> +	kfree(v);
> +
> +	if (vma->vm_file) {
> +		err = cpt_dump_dentry(&vma->vm_file->f_path, ctx);
> +		if (err < 0)
> +			return err;
> +	}
> +
> +	for (addr = vma->vm_start; addr < vma->vm_end; addr += PAGE_SIZE) {
> +		struct page_desc pd;
> +		struct cpt_page_block pgb;
> +
> +		page_get_desc(vma, addr, &pd, ctx);
> +
> +		if (pd.type == PD_FUNKEY || pd.type == PD_ABSENT) {
> +			eprintk("dump_one_vma: funkey page\n");
> +			return -EINVAL;
> +		}
> +
> +		pgb.cpt_start = addr;
> +		pgb.cpt_end = addr + PAGE_SIZE;
> +		dump_page_block(vma, &pgb, ctx);

Error handling?

> +	}
> +
> +	return 0;
> +}
> +
> +static int cpt_dump_mm_context(struct mm_struct *mm, struct cpt_context *ctx)
> +{
> +#ifdef CONFIG_X86
> +	if (mm->context.size) {
> +		struct cpt_obj_bits b;
> +		int size;
> +
> +		mutex_lock(&mm->context.lock);
> +
> +		b.cpt_type = CPT_OBJ_BITS;
> +		b.cpt_len = sizeof(b);
> +		b.cpt_content = CPT_CONTENT_MM_CONTEXT;
> +		b.cpt_size = mm->context.size * LDT_ENTRY_SIZE;
> +
> +		ctx->write(&b, sizeof(b), ctx);
> +
> +		size = mm->context.size * LDT_ENTRY_SIZE;
> +
> +		ctx->write(mm->context.ldt, size, ctx);

Error handling?

> +
> +		mutex_unlock(&mm->context.lock);
> +	}
> +#endif
> +	return 0;
> +}
> +
> +int cpt_dump_mm(struct task_struct *tsk, struct cpt_context *ctx)
> +{
> +	struct mm_struct *mm = tsk->mm;
> +	struct cpt_mm_image *v;
> +	struct vm_area_struct *vma;
> +	int err;
> +
> +	v = kzalloc(sizeof(*v), GFP_KERNEL);
> +	if (!v)
> +		return -ENOMEM;
> +
> +	v->cpt_len = sizeof(*v);
> +	v->cpt_type = CPT_OBJ_MM;
> +	v->cpt_hdrlen = sizeof(*v);
> +	v->cpt_content = CPT_CONTENT_ARRAY;
> +
> +	down_read(&mm->mmap_sem);
> +	v->cpt_start_code = mm->start_code;
> +	v->cpt_end_code = mm->end_code;
> +	v->cpt_start_data = mm->start_data;
> +	v->cpt_end_data = mm->end_data;
> +	v->cpt_start_brk = mm->start_brk;
> +	v->cpt_brk = mm->brk;
> +	v->cpt_start_stack = mm->start_stack;
> +	v->cpt_start_arg = mm->arg_start;
> +	v->cpt_end_arg = mm->arg_end;
> +	v->cpt_start_env = mm->env_start;
> +	v->cpt_end_env = mm->env_end;
> +	v->cpt_def_flags = mm->def_flags;
> +	v->cpt_flags = mm->flags;
> +	v->cpt_map_count = mm->map_count;
> +
> +	err = ctx->write(v, sizeof(*v), ctx);
> +	kfree(v);
> +	
> +	if (err) {
> +		eprintk("error during writing mm\n");
> +		goto err_up;
> +	}
> +	
> +	for (vma = mm->mmap; vma; vma = vma->vm_next) {
> +		if ((err = dump_one_vma(mm, vma, ctx)) != 0)
> +			goto err_up;
> +	}
> +
> +	err = cpt_dump_mm_context(mm, ctx);
> +
> +err_up:
> +	up_read(&mm->mmap_sem);
> +
> +	return err;
> +}
> +

[...]

Louis

-- 
Dr Louis Rilling			Kerlabs
Skype: louis.rilling			Batiment Germanium
Phone: (+33|0) 6 80 89 08 23		80 avenue des Buttes de Coesmes
http://www.kerlabs.com/			35700 Rennes

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