Hi folks,
Please help confirm if VMware backdoor Pseudo-PMCs [*] are still available
when the KVM module parameter eneble_pmu=0.
- VMWARE_BACKDOOR_PMC_HOST_TSC;
- VMWARE_BACKDOOR_PMC_REAL_TIME;
- VMWARE_BACKDOOR_PMC_APPARENT_TIME;
I'd like to say yes, but safely you have the official right to define it. Thanks.
[*] https://www.vmware.com/files/pdf/techpaper/Timekeeping-In-VirtualMachines.pdf
On 24/8/2023 4:35 am, Sean Christopherson wrote:
On Tue, Aug 22, 2023, Like Xu wrote:
From: Like Xu <likexu@xxxxxxxxxxx>
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.
Is there a real world need for this? Per commit 672ff6cff80c ("KVM: x86: Raise
#GP when guest vCPU do not support PMU"), KVM's behavior is intentional. If there
is a real world need, then (a) that justification needs to be provided, (b) this
needs a Fixes:, and (c) this probably needs to be tagged for stable.
Cc: Arbel Moshe <arbel.moshe@xxxxxxxxxx>
Cc: Liran Alon <liran.alon@xxxxxxxxxx>
Cc: Nikita Leshenko <nikita.leshchenko@xxxxxxxxxx>
The expectation is that a Cc: in the changelog means the patch email is Cc'd to
that person, i.e. one of the purposes of Cc: here is to record that people who
might care about the patch have been made aware of its existence. stable@ is
pretty much the only exception to that rule, as "Cc: stable@xxxxxxxxxxxxxxx" is
really just a metadata tag for scripts.
FWIW, I believe Liran no longer works for Oracle, no idea about the others.
Signed-off-by: Like Xu <likexu@xxxxxxxxxxx>
---
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
