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backport exposing FLUSHBYASID when running nested VMs on AMD CPUs

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this exposes the FLUSHBYASID CPU flag to nested VMs when running on an
AMD CPU. also reverts a made up check that would advertise
FLUSHBYASID as not supported. this enable certain modern hypervisors
such as VMWare ESXi 7 and Workstation 17 to run nested VMs properly
again.

Signed-off-by: Stefan Sterz <s.sterz@proxmox.com>
This commit is contained in:
Stefan Sterz 2023-10-19 16:59:12 +02:00 committed by Thomas Lamprecht
parent a5f38dcb1b
commit 3202de9857
2 changed files with 88 additions and 0 deletions
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49
patches/kernel/0014-Revert-nSVM-Check-for-reserved-encodings-of-TLB_CONT.patch Normal file
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@ -0,0 +1,49 @@
From 379ad2e0326c55682d0bb9391f16f1072fe400d2 Mon Sep 17 00:00:00 2001
From: Stefan Sterz <s.sterz@proxmox.com>
Date: Wed, 18 Oct 2023 10:45:45 +0200
Subject: [PATCH 1/2] Revert "nSVM: Check for reserved encodings of TLB_CONTROL
in nested VMCB"
This reverts commit 174a921b6975ef959dd82ee9e8844067a62e3ec1.
Signed-off-by: Stefan Sterz <s.sterz@proxmox.com>
---
arch/x86/kvm/svm/nested.c | 15 ---------------
1 file changed, 15 deletions(-)
diff --git a/arch/x86/kvm/svm/nested.c b/arch/x86/kvm/svm/nested.c
index add65dd59756..61a6c0235519 100644
--- a/arch/x86/kvm/svm/nested.c
+++ b/arch/x86/kvm/svm/nested.c
@@ -242,18 +242,6 @@ static bool nested_svm_check_bitmap_pa(struct kvm_vcpu *vcpu, u64 pa, u32 size)
kvm_vcpu_is_legal_gpa(vcpu, addr + size - 1);
}
-static bool nested_svm_check_tlb_ctl(struct kvm_vcpu *vcpu, u8 tlb_ctl)
-{
- /* Nested FLUSHBYASID is not supported yet. */
- switch(tlb_ctl) {
- case TLB_CONTROL_DO_NOTHING:
- case TLB_CONTROL_FLUSH_ALL_ASID:
- return true;
- default:
- return false;
- }
-}
-
static bool __nested_vmcb_check_controls(struct kvm_vcpu *vcpu,
struct vmcb_ctrl_area_cached *control)
{
@@ -273,9 +261,6 @@ static bool __nested_vmcb_check_controls(struct kvm_vcpu *vcpu,
IOPM_SIZE)))
return false;
- if (CC(!nested_svm_check_tlb_ctl(vcpu, control->tlb_ctl)))
- return false;
-
return true;
}
--
2.39.2

39
patches/kernel/0015-KVM-nSVM-Advertise-support-for-flush-by-ASID.patch Normal file
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@ -0,0 +1,39 @@
From 42af81abf0b96ab661591d024aed55c05dd85b91 Mon Sep 17 00:00:00 2001
From: Sean Christopherson <seanjc@google.com>
Date: Wed, 18 Oct 2023 12:41:04 -0700
Subject: [PATCH 2/2] KVM: nSVM: Advertise support for flush-by-ASID
Advertise support for FLUSHBYASID when nested SVM is enabled, as KVM can
always emulate flushing TLB entries for a vmcb12 ASID, e.g. by running L2
with a new, fresh ASID in vmcb02. Some modern hypervisors, e.g. VMWare
Workstation 17, require FLUSHBYASID support and will refuse to run if it's
not present.
Punt on proper support, as "Honor L1's request to flush an ASID on nested
VMRUN" is one of the TODO items in the (incomplete) list of issues that
need to be addressed in order for KVM to NOT do a full TLB flush on every
nested SVM transition (see nested_svm_transition_tlb_flush()).
Reported-by: Stefan Sterz <s.sterz@proxmox.com>
Closes: https://lkml.kernel.org/r/b9915c9c-4cf6-051a-2d91-44cc6380f455%40proxmox.com
Signed-off-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Stefan Sterz <s.sterz@proxmox.com>
---
arch/x86/kvm/svm/svm.c | 1 +
1 file changed, 1 insertion(+)
diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
index 9a194aa1a75a..0fde9b0c464b 100644
--- a/arch/x86/kvm/svm/svm.c
+++ b/arch/x86/kvm/svm/svm.c
@@ -4880,6 +4880,7 @@ static __init void svm_set_cpu_caps(void)
if (nested) {
kvm_cpu_cap_set(X86_FEATURE_SVM);
kvm_cpu_cap_set(X86_FEATURE_VMCBCLEAN);
+ kvm_cpu_cap_set(X86_FEATURE_FLUSHBYASID);
if (nrips)
kvm_cpu_cap_set(X86_FEATURE_NRIPS);
--
2.39.2