| Message ID | 20220422210546.458943-2-dmatlack@google.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | KVM: Extend Eager Page Splitting to the shadow MMU | expand |
On 2022/4/23 05:05, David Matlack wrote: > Commit fb58a9c345f6 ("KVM: x86/mmu: Optimize MMU page cache lookup for > fully direct MMUs") skipped the unsync checks and write flood clearing > for full direct MMUs. We can extend this further to skip the checks for > all direct shadow pages. Direct shadow pages in indirect MMUs (i.e. > shadow paging) are used when shadowing a guest huge page with smaller > pages. Such direct shadow pages, like their counterparts in fully direct > MMUs, are never marked unsynced or have a non-zero write-flooding count. > > Checking sp->role.direct also generates better code than checking > direct_map because, due to register pressure, direct_map has to get > shoved onto the stack and then pulled back off. > > No functional change intended. > > Reviewed-by: Sean Christopherson <seanjc@google.com> > Reviewed-by: Peter Xu <peterx@redhat.com> > Signed-off-by: David Matlack <dmatlack@google.com> Reviewed-by: Lai Jiangshan <jiangshanlai@gmail.com>
diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c index 69a30d6d1e2b..3de4cce317e4 100644 --- a/arch/x86/kvm/mmu/mmu.c +++ b/arch/x86/kvm/mmu/mmu.c @@ -2028,7 +2028,6 @@ static struct kvm_mmu_page *kvm_mmu_get_page(struct kvm_vcpu *vcpu, int direct, unsigned int access) { - bool direct_mmu = vcpu->arch.mmu->root_role.direct; union kvm_mmu_page_role role; struct hlist_head *sp_list; unsigned quadrant; @@ -2070,7 +2069,8 @@ static struct kvm_mmu_page *kvm_mmu_get_page(struct kvm_vcpu *vcpu, continue; } - if (direct_mmu) + /* unsync and write-flooding only apply to indirect SPs. */ + if (sp->role.direct) goto trace_get_page; if (sp->unsync) {
Commit fb58a9c345f6 ("KVM: x86/mmu: Optimize MMU page cache lookup for fully direct MMUs") skipped the unsync checks and write flood clearing for full direct MMUs. We can extend this further to skip the checks for all direct shadow pages. Direct shadow pages in indirect MMUs (i.e. shadow paging) are used when shadowing a guest huge page with smaller pages. Such direct shadow pages, like their counterparts in fully direct MMUs, are never marked unsynced or have a non-zero write-flooding count. Checking sp->role.direct also generates better code than checking direct_map because, due to register pressure, direct_map has to get shoved onto the stack and then pulled back off. No functional change intended. Reviewed-by: Sean Christopherson <seanjc@google.com> Reviewed-by: Peter Xu <peterx@redhat.com> Signed-off-by: David Matlack <dmatlack@google.com> --- arch/x86/kvm/mmu/mmu.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) base-commit: 150866cd0ec871c765181d145aa0912628289c8a