On 1/7/22 09:25, Vihas Mak wrote:
mmu_try_to_unsync_pages() performs !can_unsync check before attempting
to unsync any shadow pages.
This check is peformed inside the loop right now.
It's redundant to perform it every iteration if can_unsync is true, as
can_unsync parameter isn't getting updated inside the loop.
Move the check outside of the loop.
Same is the case with prefetch.
The meaning changes if the loop does not execute at all. Is this safe?
Paolo
Signed-off-by: Vihas Mak<makvihas@xxxxxxxxx>
Cc: Sean Christopherson<seanjc@xxxxxxxxxx>
Cc: Vitaly Kuznetsov<vkuznets@xxxxxxxxxx>
Cc: Wanpeng Li<wanpengli@xxxxxxxxxxx>
Cc: Jim Mattson<jmattson@xxxxxxxxxx>
Cc: Joerg Roedel<joro@xxxxxxxxxx>
---
arch/x86/kvm/mmu/mmu.c | 11 +++++------
1 file changed, 5 insertions(+), 6 deletions(-)
diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
index 1d275e9d7..53f4b8b07 100644
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -2586,6 +2586,11 @@ int mmu_try_to_unsync_pages(struct kvm *kvm, const struct kvm_memory_slot *slot,
if (kvm_slot_page_track_is_active(kvm, slot, gfn, KVM_PAGE_TRACK_WRITE))
return -EPERM;
+ if (!can_unsync)
+ return -EPERM;
+
+ if (prefetch)
+ return -EEXIST;
/*
* The page is not write-tracked, mark existing shadow pages unsync
* unless KVM is synchronizing an unsync SP (can_unsync = false). In
@@ -2593,15 +2598,9 @@ int mmu_try_to_unsync_pages(struct kvm *kvm, const struct kvm_memory_slot *slot,
* allowing shadow pages to become unsync (writable by the guest).
*/
for_each_gfn_indirect_valid_sp(kvm, sp, gfn) {
- if (!can_unsync)
- return -EPERM;
-
if (sp->unsync)
continue;
- if (prefetch)
- return -EEXIST;
-
