57 lines
2.0 KiB
Diff
57 lines
2.0 KiB
Diff
From a0212ec7cc4bc2f88c4435cca881d21f2b079a80 Mon Sep 17 00:00:00 2001
|
|
From: Paolo Bonzini <pbonzini@redhat.com>
|
|
Date: Thu, 26 Oct 2017 09:13:27 +0200
|
|
Subject: [PATCH 14/14] KVM: SVM: obey guest PAT
|
|
MIME-Version: 1.0
|
|
Content-Type: text/plain; charset=UTF-8
|
|
Content-Transfer-Encoding: 8bit
|
|
|
|
For many years some users of assigned devices have reported worse
|
|
performance on AMD processors with NPT than on AMD without NPT,
|
|
Intel or bare metal.
|
|
|
|
The reason turned out to be that SVM is discarding the guest PAT
|
|
setting and uses the default (PA0=PA4=WB, PA1=PA5=WT, PA2=PA6=UC-,
|
|
PA3=UC). The guest might be using a different setting, and
|
|
especially might want write combining but isn't getting it
|
|
(instead getting slow UC or UC- accesses).
|
|
|
|
Thanks a lot to geoff@hostfission.com for noticing the relation
|
|
to the g_pat setting. The patch has been tested also by a bunch
|
|
of people on VFIO users forums.
|
|
|
|
Fixes: 709ddebf81cb40e3c36c6109a7892e8b93a09464
|
|
Fixes: https://bugzilla.kernel.org/show_bug.cgi?id=196409
|
|
Cc: stable@vger.kernel.org
|
|
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
|
|
Reviewed-by: David Hildenbrand <david@redhat.com>
|
|
Tested-by: Nick Sarnie <commendsarnex@gmail.com>
|
|
Signed-off-by: Radim Krčmář <rkrcmar@redhat.com>
|
|
(cherry picked from commit 15038e14724799b8c205beb5f20f9e54896013c3)
|
|
Signed-off-by: Fabian Grünbichler <f.gruenbichler@proxmox.com>
|
|
---
|
|
arch/x86/kvm/svm.c | 7 +++++++
|
|
1 file changed, 7 insertions(+)
|
|
|
|
diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
|
|
index af256b786a70..af09baa3d736 100644
|
|
--- a/arch/x86/kvm/svm.c
|
|
+++ b/arch/x86/kvm/svm.c
|
|
@@ -3626,6 +3626,13 @@ static int svm_set_msr(struct kvm_vcpu *vcpu, struct msr_data *msr)
|
|
u32 ecx = msr->index;
|
|
u64 data = msr->data;
|
|
switch (ecx) {
|
|
+ case MSR_IA32_CR_PAT:
|
|
+ if (!kvm_mtrr_valid(vcpu, MSR_IA32_CR_PAT, data))
|
|
+ return 1;
|
|
+ vcpu->arch.pat = data;
|
|
+ svm->vmcb->save.g_pat = data;
|
|
+ mark_dirty(svm->vmcb, VMCB_NPT);
|
|
+ break;
|
|
case MSR_IA32_TSC:
|
|
kvm_write_tsc(vcpu, msr);
|
|
break;
|
|
--
|
|
2.14.2
|
|
|