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SubjectRe: Hugepages demand paging V1 [2/4]: set_huge_pte() arch updates
On Fri, 22 Oct 2004, William Lee Irwin III wrote:

> update_mmu_cache() is stage (3). Linux' software pagetable
> modifications are step (2). Generally, architectures are trying to fold
> stages (2) and (3) together in set_huge_pte(), so update_mmu_cache() is
> not so much of an issue for them (and it's actually incorrect to do
> this multiple times or without the architectures' awareness of hugepages
> in update_mmu_cache() and so on). To completely regularize the hugetlb
> case, merely move the commitment to cpu-native structures or other TLB
> insertion done within set_huge_pte() to a new case in update_mmu_cache()
> for large pages.

Ok. I have done so in the following patch but no for all archs yet. Will
work on that next week and then post V2 of the patch.

> What is in fact far more pressing is flush_dcache_page(), without a
> correct implementation of which for hugetlb, user-visible data
> corruption follows.

When is flush_dcache_page used on a huge page?

It seems that the i386 simply does nothing for flush_dcache_page. IA64
defers to update_mmu_cache by setting PG_arch_1. So these two are ok as
is.

The other archs are likely much more involved than this. I tried to find
an simple way to identify a page as a huge page via struct page but
that is not that easy and its likely not good to follow
pointers to pointers in such a critical function. Maybe we need to add a
new page flag?

Index: linux-2.6.9/arch/ia64/mm/init.c
===================================================================
--- linux-2.6.9.orig/arch/ia64/mm/init.c 2004-10-21 12:01:21.000000000 -0700
+++ linux-2.6.9/arch/ia64/mm/init.c 2004-10-22 13:07:36.000000000 -0700
@@ -95,6 +95,26 @@
set_bit(PG_arch_1, &page->flags); /* mark page as clean */
}

+void
+huge_update_mmu_cache_hpte (struct vm_area_struct *vma, unsigned long vaddr, pte_t pte)
+{
+ unsigned long addr;
+ struct page *page;
+
+ if (!pte_exec(pte))
+ return; /* not an executable page... */
+
+ page = pte_page(pte);
+ /* don't use VADDR: it may not be mapped on this CPU (or may have just been flushed): */
+ addr = (unsigned long) page_address(page);
+
+ if (test_bit(PG_arch_1, &page->flags))
+ return; /* i-cache is already coherent with d-cache */
+
+ flush_icache_range(addr, addr + HPAGE_SIZE);
+ set_bit(PG_arch_1, &page->flags); /* mark page as clean */
+}
+
inline void
ia64_set_rbs_bot (void)
{
Index: linux-2.6.9/include/asm-ia64/pgtable.h
===================================================================
--- linux-2.6.9.orig/include/asm-ia64/pgtable.h 2004-10-21 12:01:24.000000000 -0700
+++ linux-2.6.9/include/asm-ia64/pgtable.h 2004-10-22 13:23:55.000000000 -0700
@@ -482,6 +482,7 @@
* flushing that may be necessary.
*/
extern void update_mmu_cache (struct vm_area_struct *vma, unsigned long vaddr, pte_t pte);
+extern void huge_update_mmu_cache (struct vm_area_struct *vma, unsigned long vaddr, pte_t pte);

#define __HAVE_ARCH_PTEP_SET_ACCESS_FLAGS
/*
Index: linux-2.6.9/include/asm-i386/pgtable.h
===================================================================
--- linux-2.6.9.orig/include/asm-i386/pgtable.h 2004-10-21 12:01:24.000000000 -0700
+++ linux-2.6.9/include/asm-i386/pgtable.h 2004-10-22 13:09:46.000000000 -0700
@@ -389,6 +389,7 @@
* bit at the same time.
*/
#define update_mmu_cache(vma,address,pte) do { } while (0)
+#define huge_update_mmu_cache(vma,address,pte) do { } while (0)
#define __HAVE_ARCH_PTEP_SET_ACCESS_FLAGS
#define ptep_set_access_flags(__vma, __address, __ptep, __entry, __dirty) \
do { \
Index: linux-2.6.9/include/asm-sparc64/pgtable.h
===================================================================
--- linux-2.6.9.orig/include/asm-sparc64/pgtable.h 2004-10-18 14:53:06.000000000 -0700
+++ linux-2.6.9/include/asm-sparc64/pgtable.h 2004-10-22 13:13:40.000000000 -0700
@@ -347,6 +347,7 @@

struct vm_area_struct;
extern void update_mmu_cache(struct vm_area_struct *, unsigned long, pte_t);
+extern void huge_update_mmu_cache(struct vm_area_struct *, unsigned long, pte_t);

/* Make a non-present pseudo-TTE. */
static inline pte_t mk_pte_io(unsigned long page, pgprot_t prot, int space)
Index: linux-2.6.9/include/asm-sh64/pgtable.h
===================================================================
--- linux-2.6.9.orig/include/asm-sh64/pgtable.h 2004-10-21 12:01:24.000000000 -0700
+++ linux-2.6.9/include/asm-sh64/pgtable.h 2004-10-22 13:11:52.000000000 -0700
@@ -462,6 +462,7 @@

extern void update_mmu_cache(struct vm_area_struct * vma,
unsigned long address, pte_t pte);
+#define huge_update_mmu_cache update_mmu_cache

/* Encode and decode a swap entry */
#define __swp_type(x) (((x).val & 3) + (((x).val >> 1) & 0x3c))
-
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