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x86, cpa: make the kernel physical mapping initialization a two pass …
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…sequence, fix

Jeremy Fitzhardinge wrote:

> I'd noticed that current tip/master hasn't been booting under Xen, and I
> just got around to bisecting it down to this change.
>
> commit 065ae73c5462d42e9761afb76f2b52965ff45bd6
> Author: Suresh Siddha <suresh.b.siddha@intel.com>
>
>    x86, cpa: make the kernel physical mapping initialization a two pass sequence
>
> This patch is causing Xen to fail various pagetable updates because it
> ends up remapping pagetables to RW, which Xen explicitly prohibits (as
> that would allow guests to make arbitrary changes to pagetables, rather
> than have them mediated by the hypervisor).

Instead of making init a two pass sequence, to satisfy the Intel's TLB
Application note (developer.intel.com/design/processor/applnots/317080.pdf
Section 6 page 26), we preserve the original page permissions
when fragmenting the large mappings and don't touch the existing memory
mapping (which satisfies Xen's requirements).

Only open issue is: on a native linux kernel, we will go back to mapping
the first 0-1GB kernel identity mapping as executable (because of the
static mapping setup in head_64.S). We can fix this in a different
patch if needed.

Signed-off-by: Suresh Siddha <suresh.b.siddha@intel.com>
Acked-by: Jeremy Fitzhardinge <jeremy@goop.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
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Suresh Siddha authored and Ingo Molnar committed Oct 10, 2008
1 parent ad2cde1 commit b27a43c
Showing 1 changed file with 61 additions and 88 deletions.
149 changes: 61 additions & 88 deletions arch/x86/mm/init_64.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -270,10 +270,9 @@ static __ref void unmap_low_page(void *adr)
early_iounmap(adr, PAGE_SIZE);
}

static int physical_mapping_iter;

static unsigned long __meminit
phys_pte_init(pte_t *pte_page, unsigned long addr, unsigned long end)
phys_pte_init(pte_t *pte_page, unsigned long addr, unsigned long end,
pgprot_t prot)
{
unsigned pages = 0;
unsigned long last_map_addr = end;
Expand All @@ -291,35 +290,40 @@ phys_pte_init(pte_t *pte_page, unsigned long addr, unsigned long end)
break;
}

/*
* We will re-use the existing mapping.
* Xen for example has some special requirements, like mapping
* pagetable pages as RO. So assume someone who pre-setup
* these mappings are more intelligent.
*/
if (pte_val(*pte))
goto repeat_set_pte;
continue;

if (0)
printk(" pte=%p addr=%lx pte=%016lx\n",
pte, addr, pfn_pte(addr >> PAGE_SHIFT, PAGE_KERNEL).pte);
pages++;
repeat_set_pte:
set_pte(pte, pfn_pte(addr >> PAGE_SHIFT, PAGE_KERNEL));
set_pte(pte, pfn_pte(addr >> PAGE_SHIFT, prot));
last_map_addr = (addr & PAGE_MASK) + PAGE_SIZE;
}

if (physical_mapping_iter == 1)
update_page_count(PG_LEVEL_4K, pages);
update_page_count(PG_LEVEL_4K, pages);

return last_map_addr;
}

static unsigned long __meminit
phys_pte_update(pmd_t *pmd, unsigned long address, unsigned long end)
phys_pte_update(pmd_t *pmd, unsigned long address, unsigned long end,
pgprot_t prot)
{
pte_t *pte = (pte_t *)pmd_page_vaddr(*pmd);

return phys_pte_init(pte, address, end);
return phys_pte_init(pte, address, end, prot);
}

static unsigned long __meminit
phys_pmd_init(pmd_t *pmd_page, unsigned long address, unsigned long end,
unsigned long page_size_mask)
unsigned long page_size_mask, pgprot_t prot)
{
unsigned long pages = 0;
unsigned long last_map_addr = end;
Expand All @@ -330,6 +334,7 @@ phys_pmd_init(pmd_t *pmd_page, unsigned long address, unsigned long end,
unsigned long pte_phys;
pmd_t *pmd = pmd_page + pmd_index(address);
pte_t *pte;
pgprot_t new_prot = prot;

if (address >= end) {
if (!after_bootmem) {
Expand All @@ -343,45 +348,58 @@ phys_pmd_init(pmd_t *pmd_page, unsigned long address, unsigned long end,
if (!pmd_large(*pmd)) {
spin_lock(&init_mm.page_table_lock);
last_map_addr = phys_pte_update(pmd, address,
end);
end, prot);
spin_unlock(&init_mm.page_table_lock);
continue;
}
goto repeat_set_pte;
/*
* If we are ok with PG_LEVEL_2M mapping, then we will
* use the existing mapping,
*
* Otherwise, we will split the large page mapping but
* use the same existing protection bits except for
* large page, so that we don't violate Intel's TLB
* Application note (317080) which says, while changing
* the page sizes, new and old translations should
* not differ with respect to page frame and
* attributes.
*/
if (page_size_mask & (1 << PG_LEVEL_2M))
continue;
new_prot = pte_pgprot(pte_clrhuge(*(pte_t *)pmd));
}

if (page_size_mask & (1<<PG_LEVEL_2M)) {
pages++;
repeat_set_pte:
spin_lock(&init_mm.page_table_lock);
set_pte((pte_t *)pmd,
pfn_pte(address >> PAGE_SHIFT, PAGE_KERNEL_LARGE));
pfn_pte(address >> PAGE_SHIFT,
__pgprot(pgprot_val(prot) | _PAGE_PSE)));
spin_unlock(&init_mm.page_table_lock);
last_map_addr = (address & PMD_MASK) + PMD_SIZE;
continue;
}

pte = alloc_low_page(&pte_phys);
last_map_addr = phys_pte_init(pte, address, end);
last_map_addr = phys_pte_init(pte, address, end, new_prot);
unmap_low_page(pte);

spin_lock(&init_mm.page_table_lock);
pmd_populate_kernel(&init_mm, pmd, __va(pte_phys));
spin_unlock(&init_mm.page_table_lock);
}
if (physical_mapping_iter == 1)
update_page_count(PG_LEVEL_2M, pages);
update_page_count(PG_LEVEL_2M, pages);
return last_map_addr;
}

static unsigned long __meminit
phys_pmd_update(pud_t *pud, unsigned long address, unsigned long end,
unsigned long page_size_mask)
unsigned long page_size_mask, pgprot_t prot)
{
pmd_t *pmd = pmd_offset(pud, 0);
unsigned long last_map_addr;

last_map_addr = phys_pmd_init(pmd, address, end, page_size_mask);
last_map_addr = phys_pmd_init(pmd, address, end, page_size_mask, prot);
__flush_tlb_all();
return last_map_addr;
}
Expand All @@ -398,6 +416,7 @@ phys_pud_init(pud_t *pud_page, unsigned long addr, unsigned long end,
unsigned long pmd_phys;
pud_t *pud = pud_page + pud_index(addr);
pmd_t *pmd;
pgprot_t prot = PAGE_KERNEL;

if (addr >= end)
break;
Expand All @@ -411,16 +430,28 @@ phys_pud_init(pud_t *pud_page, unsigned long addr, unsigned long end,
if (pud_val(*pud)) {
if (!pud_large(*pud)) {
last_map_addr = phys_pmd_update(pud, addr, end,
page_size_mask);
page_size_mask, prot);
continue;
}

goto repeat_set_pte;
/*
* If we are ok with PG_LEVEL_1G mapping, then we will
* use the existing mapping.
*
* Otherwise, we will split the gbpage mapping but use
* the same existing protection bits except for large
* page, so that we don't violate Intel's TLB
* Application note (317080) which says, while changing
* the page sizes, new and old translations should
* not differ with respect to page frame and
* attributes.
*/
if (page_size_mask & (1 << PG_LEVEL_1G))
continue;
prot = pte_pgprot(pte_clrhuge(*(pte_t *)pud));
}

if (page_size_mask & (1<<PG_LEVEL_1G)) {
pages++;
repeat_set_pte:
spin_lock(&init_mm.page_table_lock);
set_pte((pte_t *)pud,
pfn_pte(addr >> PAGE_SHIFT, PAGE_KERNEL_LARGE));
Expand All @@ -430,7 +461,8 @@ phys_pud_init(pud_t *pud_page, unsigned long addr, unsigned long end,
}

pmd = alloc_low_page(&pmd_phys);
last_map_addr = phys_pmd_init(pmd, addr, end, page_size_mask);
last_map_addr = phys_pmd_init(pmd, addr, end, page_size_mask,
prot);
unmap_low_page(pmd);

spin_lock(&init_mm.page_table_lock);
Expand All @@ -439,8 +471,7 @@ phys_pud_init(pud_t *pud_page, unsigned long addr, unsigned long end,
}
__flush_tlb_all();

if (physical_mapping_iter == 1)
update_page_count(PG_LEVEL_1G, pages);
update_page_count(PG_LEVEL_1G, pages);

return last_map_addr;
}
Expand Down Expand Up @@ -505,54 +536,15 @@ static void __init init_gbpages(void)
direct_gbpages = 0;
}

static int is_kernel(unsigned long pfn)
{
unsigned long pg_addresss = pfn << PAGE_SHIFT;

if (pg_addresss >= (unsigned long) __pa(_text) &&
pg_addresss < (unsigned long) __pa(_end))
return 1;

return 0;
}

static unsigned long __init kernel_physical_mapping_init(unsigned long start,
unsigned long end,
unsigned long page_size_mask)
{

unsigned long next, last_map_addr;
u64 cached_supported_pte_mask = __supported_pte_mask;
unsigned long cache_start = start;
unsigned long cache_end = end;

/*
* First iteration will setup identity mapping using large/small pages
* based on page_size_mask, with other attributes same as set by
* the early code in head_64.S
*
* Second iteration will setup the appropriate attributes
* as desired for the kernel identity mapping.
*
* This two pass mechanism conforms to the TLB app note which says:
*
* "Software should not write to a paging-structure entry in a way
* that would change, for any linear address, both the page size
* and either the page frame or attributes."
*
* For now, only difference between very early PTE attributes used in
* head_64.S and here is _PAGE_NX.
*/
BUILD_BUG_ON((__PAGE_KERNEL_LARGE & ~__PAGE_KERNEL_IDENT_LARGE_EXEC)
!= _PAGE_NX);
__supported_pte_mask &= ~(_PAGE_NX);
physical_mapping_iter = 1;
unsigned long next, last_map_addr = end;

repeat:
last_map_addr = cache_end;

start = (unsigned long)__va(cache_start);
end = (unsigned long)__va(cache_end);
start = (unsigned long)__va(start);
end = (unsigned long)__va(end);

for (; start < end; start = next) {
pgd_t *pgd = pgd_offset_k(start);
Expand All @@ -564,21 +556,11 @@ static unsigned long __init kernel_physical_mapping_init(unsigned long start,
next = end;

if (pgd_val(*pgd)) {
/*
* Static identity mappings will be overwritten
* with run-time mappings. For example, this allows
* the static 0-1GB identity mapping to be mapped
* non-executable with this.
*/
if (is_kernel(pte_pfn(*((pte_t *) pgd))))
goto realloc;

last_map_addr = phys_pud_update(pgd, __pa(start),
__pa(end), page_size_mask);
continue;
}

realloc:
pud = alloc_low_page(&pud_phys);
last_map_addr = phys_pud_init(pud, __pa(start), __pa(next),
page_size_mask);
Expand All @@ -590,15 +572,6 @@ static unsigned long __init kernel_physical_mapping_init(unsigned long start,
}
__flush_tlb_all();

if (physical_mapping_iter == 1) {
physical_mapping_iter = 2;
/*
* Second iteration will set the actual desired PTE attributes.
*/
__supported_pte_mask = cached_supported_pte_mask;
goto repeat;
}

return last_map_addr;
}

Expand Down

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