Re: [PATCH] x86: fix pte_flags() to only return flags, fix lguest.

From: Jeremy Fitzhardinge
Date: Tue Jul 22 2008 - 00:50:10 EST

Rusty Russell wrote:
Change a15af1c9ea2750a9ff01e51615c45950bad8221b 'x86/paravirt: add
pte_flags to just get pte flags' removed lguest's private pte_flags()
in favor of a generic one.

Unfortunately, the generic one doesn't filter out the non-flags bits:
this results in lguest creating corrupt shadow page tables and blowing
up host memory.

Since noone is supposed to use the pfn part of pte_flags(), it seems
safest to always do the filtering.

Thinking about this, I wonder if it needs to be a pv_op at all. Generality says "yes", but there are no users which set it to anything other than native_pte_flags. The point of it is to return the flags as-is, without needing more complex stuff (like Xen's mfn to pfn conversion).

In most cases, the surrounding code will be applying its own mask anyway, so making it a simple inline will allow all the masks to get folded together.

If a user which wants to do something other than return the bare flags, it would be easy enough to put the pv_op back.

Cc: Jeremy Fitzhardinge <jeremy@xxxxxxxx>
Signed-off-by: Rusty Russell <rusty@xxxxxxxxxxxxxxx>

diff -r ee1a6adad3d2 arch/x86/kernel/paravirt.c
--- a/arch/x86/kernel/paravirt.c Mon Jul 21 12:49:25 2008 +1000
+++ b/arch/x86/kernel/paravirt.c Tue Jul 22 14:09:33 2008 +1000
@@ -428,7 +428,7 @@ struct pv_mmu_ops pv_mmu_ops = {
#endif /* PAGETABLE_LEVELS >= 3 */
.pte_val = native_pte_val,
- .pte_flags = native_pte_val,
+ .pte_flags = native_pte_flags,
.pgd_val = native_pgd_val,
.make_pte = native_make_pte,
diff -r ee1a6adad3d2 include/asm-x86/page.h
--- a/include/asm-x86/page.h Mon Jul 21 12:49:25 2008 +1000
+++ b/include/asm-x86/page.h Tue Jul 22 14:09:33 2008 +1000
@@ -144,6 +144,18 @@ static inline pteval_t native_pte_val(pt
return pte.pte;
+/* This belongs in pgtable.h, but our includes are too much of a mess. */
+#if defined(CONFIG_X86_64) || defined(CONFIG_X86_PAE)
+#define PTE_FLAGS _AC(0x8000000000000FFF, ULL)
+#define PTE_FLAGS 0x00000FFF
We already have this, it's called PTE_MASK.

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