github-mirror/linux
1
0
Fork 0
mirror of https://github.com/torvalds/linux.git synced 2026-06-01 11:03:43 +02:00
Code Issues Actions Packages Projects Releases Wiki Activity Graph

KVM: x86/pmu: Disallow "fast" RDPMC for architectural Intel PMUs

Browse Source 
Inject #GP on RDPMC if the "fast" flag is set for architectural Intel
PMUs, i.e. if the PMU version is non-zero.  Per Intel's SDM, and confirmed
on bare metal, the "fast" flag is supported only for non-architectural
PMUs, and is reserved for architectural PMUs.

  If the processor does not support architectural performance monitoring
  (CPUID.0AH:EAX[7:0]=0), ECX[30:0] specifies the index of the PMC to be
  read. Setting ECX[31] selects “fast” read mode if supported. In this mode,
  RDPMC returns bits 31:0 of the PMC in EAX while clearing EDX to zero.

  If the processor does support architectural performance monitoring
  (CPUID.0AH:EAX[7:0] ≠ 0), ECX[31:16] specifies type of PMC while ECX[15:0]
  specifies the index of the PMC to be read within that type. The following
  PMC types are currently defined:
  — General-purpose counters use type 0. The index x (to read IA32_PMCx)
    must be less than the value enumerated by CPUID.0AH.EAX[15:8] (thus
    ECX[15:8] must be zero).
  — Fixed-function counters use type 4000H. The index x (to read
    IA32_FIXED_CTRx) can be used if either CPUID.0AH.EDX[4:0] > x or
    CPUID.0AH.ECX[x] = 1 (thus ECX[15:5] must be 0).
  — Performance metrics use type 2000H. This type can be used only if
    IA32_PERF_CAPABILITIES.PERF_METRICS_AVAILABLE[bit 15]=1. For this type,
    the index in ECX[15:0] is implementation specific.

Opportunistically WARN if KVM ever actually tries to complete RDPMC for a
non-architectural PMU, and drop the non-existent "support" for fast RDPMC,
as KVM doesn't support such PMUs, i.e. kvm_pmu_rdpmc() should reject the
RDPMC before getting to the Intel code.

Fixes: f5132b0138 ("KVM: Expose a version 2 architectural PMU to a guests")
Fixes: 67f4d4288c ("KVM: x86: rdpmc emulation checks the counter incorrectly")
Reviewed-by: Dapeng Mi <dapeng1.mi@linux.intel.com>
Tested-by: Dapeng Mi <dapeng1.mi@linux.intel.com>
Link: https://lore.kernel.org/r/20240109230250.424295-10-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>
This commit is contained in:
Sean Christopherson 2024-01-09 15:02:29 -08:00
parent d652981db0
commit 5728a4a0ea
1 changed files with 18 additions and 4 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

22
arch/x86/kvm/vmx/pmu_intel.c
View File

@ -27,7 +27,6 @@
* "fast" reads, whereas the "type" is an explicit value.
*/
#define INTEL_RDPMC_FIXED INTEL_PMC_FIXED_RDPMC_BASE
#define INTEL_RDPMC_FAST BIT(31)
#define MSR_PMC_FULL_WIDTH_BIT (MSR_IA32_PMC0 - MSR_IA32_PERFCTR0)
@ -72,10 +71,25 @@ static struct kvm_pmc *intel_rdpmc_ecx_to_pmc(struct kvm_vcpu *vcpu,
struct kvm_pmc *counters;
unsigned int num_counters;
if (idx & INTEL_RDPMC_FAST)
*mask &= GENMASK_ULL(31, 0);
/*
* The encoding of ECX for RDPMC is different for architectural versus
* non-architecturals PMUs (PMUs with version '0'). For architectural
* PMUs, bits 31:16 specify the PMC type and bits 15:0 specify the PMC
* index. For non-architectural PMUs, bit 31 is a "fast" flag, and
* bits 30:0 specify the PMC index.
*
* Yell and reject attempts to read PMCs for a non-architectural PMU,
* as KVM doesn't support such PMUs.
*/
if (WARN_ON_ONCE(!pmu->version))
return NULL;
idx &= ~(INTEL_RDPMC_FIXED | INTEL_RDPMC_FAST);
/*
* Fixed PMCs are supported on all architectural PMUs. Note, KVM only
* emulates fixed PMCs for PMU v2+, but the flag itself is still valid,
* i.e. let RDPMC fail due to accessing a non-existent counter.
*/
idx &= ~INTEL_RDPMC_FIXED;
if (fixed) {
counters = pmu->fixed_counters;
num_counters = pmu->nr_arch_fixed_counters;