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

Avi Kivity
2010-06-28T09:50:57Z

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@cn.fujitsu.com>
> ---
> 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);
> #define CREATE_TRACE_POINTS
> #include "mmutrace.h"
>
> -#define SPTE_HOST_WRITEABLE (1ULL<< PT_FIRST_AVAIL_BITS_SHIFT)
> +#define SPTE_HOST_WRITEABLE (1ULL<< PT_FIRST_AVAIL_BITS_SHIFT)
> +#define SPTE_NO_DIRTY (2ULL<< PT_FIRST_AVAIL_BITS_SHIFT)
>
> #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,
> break;
> }
>
> + 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&
> + PT64_BASE_ADDR_MASK);
> + 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