Re: [PATCH 09/11] KVM: MMU: simplify mmu_need_write_protect

From: Kai Huang
Date: Tue Dec 15 2015 - 03:48:04 EST




On 12/01/2015 02:26 AM, Xiao Guangrong wrote:
Now, all non-leaf shadow page are page tracked, if gfn is not tracked
there is no non-leaf shadow page of gfn is existed, we can directly
make the shadow page of gfn to unsync

Signed-off-by: Xiao Guangrong <guangrong.xiao@xxxxxxxxxxxxxxx>
---
arch/x86/kvm/mmu.c | 26 ++++++++------------------
1 file changed, 8 insertions(+), 18 deletions(-)

diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
index 5a2ca73..f89e77f 100644
--- a/arch/x86/kvm/mmu.c
+++ b/arch/x86/kvm/mmu.c
@@ -2461,41 +2461,31 @@ static void __kvm_unsync_page(struct kvm_vcpu *vcpu, struct kvm_mmu_page *sp)
kvm_mmu_mark_parents_unsync(sp);
}
-static void kvm_unsync_pages(struct kvm_vcpu *vcpu, gfn_t gfn)
+static bool kvm_unsync_pages(struct kvm_vcpu *vcpu, gfn_t gfn,
+ bool can_unsync)
{
struct kvm_mmu_page *s;
for_each_gfn_indirect_valid_sp(vcpu->kvm, s, gfn) {
+ if (!can_unsync)
+ return true;
How about moving this right before for_each_gfn_indirect_valid_sp? As can_unsync is passed as parameter, so there's no point checking it several times.

A further thinking is can we move it to mmu_need_write_protect? Passing can_unsync as parameter to kvm_unsync_pages sounds a little bit odd.

+
if (s->unsync)
continue;
WARN_ON(s->role.level != PT_PAGE_TABLE_LEVEL);
How about large page mapping? Such as if guest uses 2M mapping and its shadow is indirect, does above WARN_ON still meet? As you removed the PT level check in mmu_need_write_protect.

Thanks,
-Kai
__kvm_unsync_page(vcpu, s);
}
+
+ return false;
}

static bool mmu_need_write_protect(struct kvm_vcpu *vcpu, gfn_t gfn,
bool can_unsync)
{
- struct kvm_mmu_page *s;
- bool need_unsync = false;
-
if (kvm_page_track_check_mode(vcpu, gfn, KVM_PAGE_TRACK_WRITE))
return true;
- for_each_gfn_indirect_valid_sp(vcpu->kvm, s, gfn) {
- if (!can_unsync)
- return true;
-
- if (s->role.level != PT_PAGE_TABLE_LEVEL)
- return true;
-
- if (!s->unsync)
- need_unsync = true;
- }
- if (need_unsync)
- kvm_unsync_pages(vcpu, gfn);
-
- return false;
+ return kvm_unsync_pages(vcpu, gfn, can_unsync);
}
static bool kvm_is_mmio_pfn(pfn_t pfn)

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