Re: [PATCH v2 3/10] KVM: MMU: fix direct sp's access corruptted

From: Avi Kivity
Date: Mon Jun 28 2010 - 05:51:22 EST

On 06/25/2010 03:06 PM, Xiao Guangrong wrote:
Consider using small page to fit guest's large page mapping:

If the mapping is writable but the dirty flag is not set, we will find
the read-only direct sp and setup the mapping, then if the write #PF
occur, we will mark this mapping writable in the read-only direct sp,
now, other real read-only mapping will happily write it without #PF.

It may hurt guest's COW

Fixed by re-install the mapping when write #PF occur.

Signed-off-by: Xiao Guangrong<xiaoguangrong@xxxxxxxxxxxxxx>
arch/x86/kvm/mmu.c | 3 ++-
arch/x86/kvm/paging_tmpl.h | 18 ++++++++++++++++++
2 files changed, 20 insertions(+), 1 deletions(-)

diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
index 556a798..0412ba4 100644
--- a/arch/x86/kvm/mmu.c
+++ b/arch/x86/kvm/mmu.c
@@ -153,7 +153,8 @@ module_param(oos_shadow, bool, 0644);
#include "mmutrace.h"


#define SHADOW_PT_INDEX(addr, level) PT64_INDEX(addr, level)

diff --git a/arch/x86/kvm/paging_tmpl.h b/arch/x86/kvm/paging_tmpl.h
index e46eb8a..fdba751 100644
--- a/arch/x86/kvm/paging_tmpl.h
+++ b/arch/x86/kvm/paging_tmpl.h
@@ -325,6 +325,20 @@ static u64 *FNAME(fetch)(struct kvm_vcpu *vcpu, gva_t addr,

+ if (*sptep& SPTE_NO_DIRTY) {
+ struct kvm_mmu_page *child;
+ WARN_ON(level != gw->level);
+ WARN_ON(!is_shadow_present_pte(*sptep));
+ if (dirty) {
+ child = page_header(*sptep&
+ mmu_page_remove_parent_pte(child, sptep);
+ __set_spte(sptep, shadow_trap_nonpresent_pte);
+ kvm_flush_remote_tlbs(vcpu->kvm);
+ }
+ }

Instead of adding a new bit, can you encode the protection in the direct sp's access bits? So we'll have one sp for read-only or writeable-but-not-dirty small pages, and another sp for writeable-and-dirty small pages.

error compiling committee.c: too many arguments to function

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