From: Sean Christopherson Date: Sat, 21 Dec 2024 01:16:47 +0000 (-0800) Subject: KVM: x86: Avoid double RDPKRU when loading host/guest PKRU X-Git-Tag: v6.14-rc1~94^2~4^2 X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=4c20cd4cee929aef89118ac8820cefab427c6ae1;p=thirdparty%2Fkernel%2Flinux.git KVM: x86: Avoid double RDPKRU when loading host/guest PKRU Use the raw wrpkru() helper when loading the guest/host's PKRU on switch to/from guest context, as the write_pkru() wrapper incurs an unnecessary rdpkru(). In both paths, KVM is guaranteed to have performed RDPKRU since the last possible write, i.e. KVM has a fresh cache of the current value in hardware. This effectively restores KVM's behavior to that of KVM prior to commit c806e88734b9 ("x86/pkeys: Provide *pkru() helpers"), which renamed the raw helper from __write_pkru() => wrpkru(), and turned __write_pkru() into a wrapper. Commit 577ff465f5a6 ("x86/fpu: Only write PKRU if it is different from current") then added the extra RDPKRU to avoid an unnecessary WRPKRU, but completely missed that KVM already optimized away pointless writes. Reported-by: Adrian Hunter Fixes: 577ff465f5a6 ("x86/fpu: Only write PKRU if it is different from current") Signed-off-by: Adrian Hunter Link: https://lore.kernel.org/r/20241221011647.3747448-1-seanjc@google.com Signed-off-by: Sean Christopherson --- diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index 7bbdf916a1369..46d12128f032c 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -1186,7 +1186,7 @@ void kvm_load_guest_xsave_state(struct kvm_vcpu *vcpu) vcpu->arch.pkru != vcpu->arch.host_pkru && ((vcpu->arch.xcr0 & XFEATURE_MASK_PKRU) || kvm_is_cr4_bit_set(vcpu, X86_CR4_PKE))) - write_pkru(vcpu->arch.pkru); + wrpkru(vcpu->arch.pkru); } EXPORT_SYMBOL_GPL(kvm_load_guest_xsave_state); @@ -1200,7 +1200,7 @@ void kvm_load_host_xsave_state(struct kvm_vcpu *vcpu) kvm_is_cr4_bit_set(vcpu, X86_CR4_PKE))) { vcpu->arch.pkru = rdpkru(); if (vcpu->arch.pkru != vcpu->arch.host_pkru) - write_pkru(vcpu->arch.host_pkru); + wrpkru(vcpu->arch.host_pkru); } if (kvm_is_cr4_bit_set(vcpu, X86_CR4_OSXSAVE)) {