| Message ID | 20220311002528.2230172-2-dmatlack@google.com |
|---|---|
| State | Changes Requested |
| Headers | show |
| Series | Extend Eager Page Splitting to the shadow MMU | expand |
On Fri, Mar 11, 2022 at 12:25:03AM +0000, 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 and skip the checks for > all direct shadow pages. Direct shadow pages are never marked unsynced > or have a non-zero write-flooding count. Nit: IMHO it's better to spell out the exact functional change, IIUC those are the direct mapped SPs where guest uses huge pages but host uses only small pages for the shadowing? > > Checking sp->role.direct alos 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> > Signed-off-by: David Matlack <dmatlack@google.com> Reviewed-by: Peter Xu <peterx@redhat.com>
On Tue, Mar 15, 2022 at 12:40 AM Peter Xu <peterx@redhat.com> wrote: > > On Fri, Mar 11, 2022 at 12:25:03AM +0000, 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 and skip the checks for > > all direct shadow pages. Direct shadow pages are never marked unsynced > > or have a non-zero write-flooding count. > > Nit: IMHO it's better to spell out the exact functional change, IIUC those > are the direct mapped SPs where guest uses huge pages but host uses only > small pages for the shadowing? Yes that's correct. I'll include that in the commit message in the next version. > > > > > Checking sp->role.direct alos 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> > > Signed-off-by: David Matlack <dmatlack@google.com> > > Reviewed-by: Peter Xu <peterx@redhat.com> > > -- > Peter Xu >
diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c index 3b8da8b0745e..3ad67f70e51c 100644 --- a/arch/x86/kvm/mmu/mmu.c +++ b/arch/x86/kvm/mmu/mmu.c @@ -2034,7 +2034,6 @@ static struct kvm_mmu_page *kvm_mmu_get_page(struct kvm_vcpu *vcpu, int direct, unsigned int access) { - bool direct_mmu = vcpu->arch.mmu->direct_map; union kvm_mmu_page_role role; struct hlist_head *sp_list; unsigned quadrant; @@ -2075,7 +2074,8 @@ 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 and skip the checks for all direct shadow pages. Direct shadow pages are never marked unsynced or have a non-zero write-flooding count. Checking sp->role.direct alos 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> Signed-off-by: David Matlack <dmatlack@google.com> --- arch/x86/kvm/mmu/mmu.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) base-commit: ce41d078aaa9cf15cbbb4a42878cc6160d76525e