linux-kernel - [PATCH] KVM: x86: Allow exposure of VMware backdoor Pseudo-PMCs when !enable

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Date:   Tue, 22 Aug 2023 16:03:12 +0800
From:   Like Xu <like.xu.linux@...il.com>
To:     Sean Christopherson <seanjc@...gle.com>
Cc:     Paolo Bonzini <pbonzini@...hat.com>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: [PATCH] KVM: x86: Allow exposure of VMware backdoor Pseudo-PMCs when !enable_pmu

From: Like Xu <likexu@...cent.com>

Fix kvm_pmu_rdpmc() logic to allow exposure of VMware backdoor Pseudo-PMCs
if pmu is globally disabled.

In this usage scenario, once vmware_backdoor is enabled, the VMs can fully
utilize all of the vmware_backdoor-related resources, not just part of it,
i.e., vcpu should always be able to access the VMware backdoor Pseudo-PMCs
via RDPMC. Since the enable_pmu is more concerned with the visibility of
hardware pmu resources on the host, fix it to decouple the two knobs.

The test case vmware_backdoors from KUT is used for validation.

Cc: Arbel Moshe <arbel.moshe@...cle.com>
Cc: Liran Alon <liran.alon@...cle.com>
Cc: Nikita Leshenko <nikita.leshchenko@...cle.com>
Signed-off-by: Like Xu <likexu@...cent.com>
---
 arch/x86/kvm/pmu.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/arch/x86/kvm/pmu.c b/arch/x86/kvm/pmu.c
index edb89b51b383..c896328b2b5a 100644
--- a/arch/x86/kvm/pmu.c
+++ b/arch/x86/kvm/pmu.c
@@ -526,12 +526,12 @@ int kvm_pmu_rdpmc(struct kvm_vcpu *vcpu, unsigned idx, u64 *data)
 	struct kvm_pmc *pmc;
 	u64 mask = fast_mode ? ~0u : ~0ull;

-	if (!pmu->version)
-		return 1;
-
 	if (is_vmware_backdoor_pmc(idx))
 		return kvm_pmu_rdpmc_vmware(vcpu, idx, data);

+	if (!pmu->version)
+		return 1;
+
 	pmc = static_call(kvm_x86_pmu_rdpmc_ecx_to_pmc)(vcpu, idx, &mask);
 	if (!pmc)
 		return 1;

base-commit: fff2e47e6c3b8050ca26656693caa857e3a8b740
-- 
2.41.0