linux-kernel - [PATCH] x86: fix pte_flags() to only return flags, fix lguest (updated)

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Message-Id: <200807221540.47161.rusty@rustcorp.com.au>
Date:	Tue, 22 Jul 2008 15:40:46 +1000
From:	Rusty Russell <rusty@...tcorp.com.au>
To:	Jeremy Fitzhardinge <jeremy@...p.org>
Cc:	Ingo Molnar <mingo@...e.hu>, linux-kernel@...r.kernel.org
Subject: [PATCH] x86: fix pte_flags() to only return flags, fix lguest (updated)

(Jeremy said:
	rusty: use PTE_MASK
	rusty: use PTE_MASK
	rusty: use PTE_MASK
 When I asked:
	jsgf: does that include the NX flag?
 He responded eloquently:
	rusty: use PTE_MASK
	rusty: use PTE_MASK
	yes, it's the official constant of masking flags out of ptes
)

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.

Cc: Jeremy Fitzhardinge <jeremy@...p.org>
Signed-off-by: Rusty Russell <rusty@...tcorp.com.au>

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 15:31:04 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 15:31:04 2008 +1000
@@ -144,6 +144,11 @@ static inline pteval_t native_pte_val(pt
 	return pte.pte;
 }
 
+static inline pteval_t native_pte_flags(pte_t pte)
+{
+	return native_pte_val(pte) & ~PTE_MASK;
+}
+
 #define pgprot_val(x)	((x).pgprot)
 #define __pgprot(x)	((pgprot_t) { (x) } )
 
@@ -165,7 +170,7 @@ static inline pteval_t native_pte_val(pt
 #endif
 
 #define pte_val(x)	native_pte_val(x)
-#define pte_flags(x)	native_pte_val(x)
+#define pte_flags(x)	native_pte_flags(x)
 #define __pte(x)	native_make_pte(x)
 
 #endif	/* CONFIG_PARAVIRT */
diff -r ee1a6adad3d2 include/asm-x86/paravirt.h
--- a/include/asm-x86/paravirt.h	Mon Jul 21 12:49:25 2008 +1000
+++ b/include/asm-x86/paravirt.h	Tue Jul 22 15:31:04 2008 +1000
@@ -1083,6 +1083,9 @@ static inline pteval_t pte_flags(pte_t p
 		ret = PVOP_CALL1(pteval_t, pv_mmu_ops.pte_flags,
 				 pte.pte);
 
+#ifdef CONFIG_PARAVIRT_DEBUG
+	BUG_ON(ret & PTE_MASK);
+#endif
 	return ret;
 }
 
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