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Subject[UPDATED] Re: [PATCH 1/5] Add pagetable allocation notifiers
Chris Wright wrote:

>* Zachary Amsden (zach@vmware.com) wrote:
>
>
>>Chris Wright wrote:
>>
>>
>>
>>>* Zachary Amsden (zach@vmware.com) wrote:
>>>
>>>
>>>
>>>
>>>>--- linux-2.6.13.orig/arch/i386/mm/init.c 2005-08-24
>>>>09:31:05.000000000 -0700
>>>>+++ linux-2.6.13/arch/i386/mm/init.c 2005-08-24 09:31:31.000000000 -0700
>>>>@@ -79,6 +79,7 @@ static pte_t * __init one_page_table_ini
>>>>{
>>>> if (pmd_none(*pmd)) {
>>>> pte_t *page_table = (pte_t *)
>>>> alloc_bootmem_low_pages(PAGE_SIZE);
>>>>+ SetPagePTE(virt_to_page(page_table));
>>>>
>>>>
>>>>
>>>>
>>>Xen has this on one_md_table_init() as well for pmd.
>>>
>>>
>>I'll add that in another patch. It's easy to miss some of the init time
>>call sites (we don't actually depend on them for correctness).
>>
>>
>
>You could just respin this patch.
>
>

Done. Looks like you want empty_zero_page write protected too. That
seems like a fine idea to me unless something really wants to do atomic
64-bit reads on it.

>>>>
>>>>
>>>Why the switch of kmem_cache_free call?
>>>
>>>
>>Because pgd_val(pgd[i])-1 is confusing.
>>
>>
>
>Yes, I agree it is. That's why I was wondering about the ClearPagePDE calls
>which don't use them.
>
>

The -1 is quite useless when you're going to shift >> 12 anyways to get
a frame number to index into mem_map, which is why they are not there.
Plus, it just seems scary if you got it wrong - let's say you had a not
present page - not that you could, but now you are freeing a misaligned
address in the _previous_ page. I really don't like that -1 at all. I
will clean it up, but it does certainly deserve another patch.

>
>
>>Using (pgd_val(pgd[i]) -
>>_PAGE_PRESENT) would be better, but the +/- 1s all over the place here
>>could use some general cleanup as well. I smell a cleanup fit coming
>>on. Using (pgd_val(pgd[i]) & PAGE_MASK) is a less error prone way to
>>get the physical frame bits, since it is not wrong if you turn on PCD or
>>PWD.
>>
>>
>
>Please save all that for later cleanup. As it stands it's just a conversion
>of one random call site, which should be dropped from the patch.
>
>

Working on it now.
Hooks are provided for the mach-XXX subarchitecture at the time prior to a
page being used as a page table at all levels, for PAE and non-PAE kernels.
Note that in PAE mode, multiple PDP roots may exist on the same page with
other data, so the root must be shadowed instead. This is not a performance
issue, since PAE only uses 4 top level PDPEs.

The hooks are:

SetPagePTE(ppn) - indicates that a given physical page is going to be used
as a page table.

SetPagePDE(ppn) - indicates that a given physical page is going to be used
as a page directory.

ClearPageXXX(ppn) - indicates that the physical page is now done being
used as a certain type of page.

These hooks can be used in two ways; for shadow mode, they serve as
requests to pre-allocate and deallocate shadow page tables, and for
direct page table mode, they serve as write protect/unprotect requests.

Signed-off-by: Zachary Amsden <zach@vmware.com>
Patch-subject: Add pagetable allocation notifiers
Index: linux-2.6.13/arch/i386/mm/init.c
===================================================================
--- linux-2.6.13.orig/arch/i386/mm/init.c 2005-08-24 14:34:30.000000000 -0700
+++ linux-2.6.13/arch/i386/mm/init.c 2005-08-24 14:35:50.000000000 -0700
@@ -59,6 +59,7 @@ static pmd_t * __init one_md_table_init(

#ifdef CONFIG_X86_PAE
pmd_table = (pmd_t *) alloc_bootmem_low_pages(PAGE_SIZE);
+ SetPagePDE(virt_to_page(pmd_table));
set_pgd(pgd, __pgd(__pa(pmd_table) | _PAGE_PRESENT));
pud = pud_offset(pgd, 0);
if (pmd_table != pmd_offset(pud, 0))
@@ -79,6 +80,7 @@ static pte_t * __init one_page_table_ini
{
if (pmd_none(*pmd)) {
pte_t *page_table = (pte_t *) alloc_bootmem_low_pages(PAGE_SIZE);
+ SetPagePTE(virt_to_page(page_table));
set_pmd(pmd, __pmd(__pa(page_table) | _PAGE_TABLE));
if (page_table != pte_offset_kernel(pmd, 0))
BUG();
@@ -313,6 +315,7 @@ static void __init pagetable_init (void)
#ifdef CONFIG_X86_PAE
int i;
/* Init entries of the first-level page table to the zero page */
+ SetPagePDE(virt_to_page(empty_zero_page));
for (i = 0; i < PTRS_PER_PGD; i++)
set_pgd(pgd_base + i, __pgd(__pa(empty_zero_page) | _PAGE_PRESENT));
#endif
Index: linux-2.6.13/arch/i386/mm/pageattr.c
===================================================================
--- linux-2.6.13.orig/arch/i386/mm/pageattr.c 2005-08-24 14:34:30.000000000 -0700
+++ linux-2.6.13/arch/i386/mm/pageattr.c 2005-08-24 14:36:09.000000000 -0700
@@ -52,6 +52,7 @@ static struct page *split_large_page(uns
address = __pa(address);
addr = address & LARGE_PAGE_MASK;
pbase = (pte_t *)page_address(base);
+ SetPagePTE(virt_to_page(pbase));
for (i = 0; i < PTRS_PER_PTE; i++, addr += PAGE_SIZE) {
set_pte(&pbase[i], pfn_pte(addr >> PAGE_SHIFT,
addr == address ? prot : PAGE_KERNEL));
@@ -146,6 +147,7 @@ __change_page_attr(struct page *page, pg
BUG_ON(!page_count(kpte_page));

if (cpu_has_pse && (page_count(kpte_page) == 1)) {
+ ClearPagePTE(virt_to_page(kpte));
list_add(&kpte_page->lru, &df_list);
revert_page(kpte_page, address);
}
Index: linux-2.6.13/arch/i386/mm/pgtable.c
===================================================================
--- linux-2.6.13.orig/arch/i386/mm/pgtable.c 2005-08-24 14:34:30.000000000 -0700
+++ linux-2.6.13/arch/i386/mm/pgtable.c 2005-08-24 14:35:50.000000000 -0700
@@ -209,6 +209,7 @@ void pgd_ctor(void *pgd, kmem_cache_t *c

if (PTRS_PER_PMD == 1) {
memset(pgd, 0, USER_PTRS_PER_PGD*sizeof(pgd_t));
+ SetPagePDE(virt_to_page(pgd));
spin_lock_irqsave(&pgd_lock, flags);
}

@@ -227,6 +228,7 @@ void pgd_dtor(void *pgd, kmem_cache_t *c
{
unsigned long flags; /* can be called from interrupt context */

+ ClearPagePDE(virt_to_page(pgd));
spin_lock_irqsave(&pgd_lock, flags);
pgd_list_del(pgd);
spin_unlock_irqrestore(&pgd_lock, flags);
@@ -244,13 +246,16 @@ pgd_t *pgd_alloc(struct mm_struct *mm)
pmd_t *pmd = kmem_cache_alloc(pmd_cache, GFP_KERNEL);
if (!pmd)
goto out_oom;
+ SetPagePDE(virt_to_page(pmd));
set_pgd(&pgd[i], __pgd(1 + __pa(pmd)));
}
return pgd;

out_oom:
- for (i--; i >= 0; i--)
+ for (i--; i >= 0; i--) {
+ ClearPagePDE(pfn_to_page(pgd_val(pgd[i]) >> PAGE_SHIFT));
kmem_cache_free(pmd_cache, (void *)__va(pgd_val(pgd[i])-1));
+ }
kmem_cache_free(pgd_cache, pgd);
return NULL;
}
@@ -261,8 +266,10 @@ void pgd_free(pgd_t *pgd)

/* in the PAE case user pgd entries are overwritten before usage */
if (PTRS_PER_PMD > 1)
- for (i = 0; i < USER_PTRS_PER_PGD; ++i)
+ for (i = 0; i < USER_PTRS_PER_PGD; ++i) {
+ ClearPagePDE(pfn_to_page(pgd_val(pgd[i]) >> PAGE_SHIFT));
kmem_cache_free(pmd_cache, (void *)__va(pgd_val(pgd[i])-1));
+ }
/* in the non-PAE case, free_pgtables() clears user pgd entries */
kmem_cache_free(pgd_cache, pgd);
}
Index: linux-2.6.13/include/asm-i386/pgalloc.h
===================================================================
--- linux-2.6.13.orig/include/asm-i386/pgalloc.h 2005-08-24 14:34:30.000000000 -0700
+++ linux-2.6.13/include/asm-i386/pgalloc.h 2005-08-24 14:35:50.000000000 -0700
@@ -5,14 +5,22 @@
#include <asm/fixmap.h>
#include <linux/threads.h>
#include <linux/mm.h> /* for struct page */
+#include <mach_pgalloc.h>

-#define pmd_populate_kernel(mm, pmd, pte) \
- set_pmd(pmd, __pmd(_PAGE_TABLE + __pa(pte)))
+#define pmd_populate_kernel(mm, pmd, pte) \
+do { \
+ SetPagePTE(virt_to_page(pte)); \
+ set_pmd(pmd, __pmd(_PAGE_TABLE + __pa(pte))); \
+} while (0)

#define pmd_populate(mm, pmd, pte) \
+do { \
+ SetPagePTE(pte); \
set_pmd(pmd, __pmd(_PAGE_TABLE + \
((unsigned long long)page_to_pfn(pte) << \
- (unsigned long long) PAGE_SHIFT)))
+ (unsigned long long) PAGE_SHIFT))); \
+} while (0)
+
/*
* Allocate and free page tables.
*/
@@ -33,7 +41,11 @@ static inline void pte_free(struct page
}


-#define __pte_free_tlb(tlb,pte) tlb_remove_page((tlb),(pte))
+#define __pte_free_tlb(tlb,pte) \
+do { \
+ tlb_remove_page((tlb),(pte)); \
+ ClearPagePTE(pte); \
+} while (0)

#ifdef CONFIG_X86_PAE
/*
Index: linux-2.6.13/include/asm-i386/mach-default/mach_pgalloc.h
===================================================================
--- linux-2.6.13.orig/include/asm-i386/mach-default/mach_pgalloc.h 2005-08-24 14:34:30.000000000 -0700
+++ linux-2.6.13/include/asm-i386/mach-default/mach_pgalloc.h 2005-08-24 14:35:50.000000000 -0700
@@ -1,7 +1,40 @@
+/*
+ * Copyright (C) 2005, VMware, Inc.
+ *
+ * All rights reserved.
+ *
+ * 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; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE, GOOD TITLE or
+ * NON INFRINGEMENT. See the GNU General Public License for more
+ * details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
+ *
+ * Send feedback to zach@vmware.com
+ *
+ */
#ifndef __ASM_MACH_PGALLOC_H
#define __ASM_MACH_PGALLOC_H

+/*
+ * These hooks allow the hypervisor to be notified about page type
+ * transition events.
+ */
+
+#define SetPagePTE(_page)
+#define ClearPagePTE(_page)
+#define SetPagePDE(_page)
+#define ClearPagePDE(_page)
+
#define SetPagesLDT(_va, _pages)
#define ClearPagesLDT(_va, _pages)

-#endif
+#endif /* _ASM_MACH_PGALLOC_H */
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