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[PATCH 3/5] x86/perf: expose LBR format in PERF_CAPABILITIES
- To: xen-devel@xxxxxxxxxxxxxxxxxxxx
- From: Roger Pau Monne <roger.pau@xxxxxxxxxx>
- Date: Fri, 20 May 2022 15:37:44 +0200
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- Cc: Roger Pau Monne <roger.pau@xxxxxxxxxx>, Jan Beulich <jbeulich@xxxxxxxx>, Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, Wei Liu <wl@xxxxxxx>
- Delivery-date: Fri, 20 May 2022 13:38:19 +0000
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- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
Allow exposing the PDCM bit in CPUID for HVM guests if present on the
platform, which in turn allows exposing PERF_CAPABILITIES. Limit the
information exposed in PERF_CAPABILITIES to the LBR format only.
This is helpful as hardware without model-specific LBRs set format to
0x3f in order to notify the feature is not present.
Signed-off-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
---
Seeing as we have never exposed PDCM in CPUID I wonder whether there's
something that I'm missing that makes exposing PERF_CAPABILITIES LBR
format not as trivial as it looks.
---
xen/arch/x86/msr.c | 9 +++++++++
xen/include/public/arch-x86/cpufeatureset.h | 2 +-
2 files changed, 10 insertions(+), 1 deletion(-)
diff --git a/xen/arch/x86/msr.c b/xen/arch/x86/msr.c
index 01a15857b7..423a795d1d 100644
--- a/xen/arch/x86/msr.c
+++ b/xen/arch/x86/msr.c
@@ -316,6 +316,15 @@ int guest_rdmsr(struct vcpu *v, uint32_t msr, uint64_t
*val)
*val = 0;
break;
+ case MSR_IA32_PERF_CAPABILITIES:
+ if ( !cp->basic.pdcm )
+ goto gp_fault;
+
+ /* Only report LBR format. */
+ rdmsrl(MSR_IA32_PERF_CAPABILITIES, *val);
+ *val &= MSR_IA32_PERF_CAP_LBR_FORMAT;
+ break;
+
case MSR_X2APIC_FIRST ... MSR_X2APIC_LAST:
if ( !is_hvm_domain(d) || v != curr )
goto gp_fault;
diff --git a/xen/include/public/arch-x86/cpufeatureset.h
b/xen/include/public/arch-x86/cpufeatureset.h
index cd6409f9f3..5fdaec43c5 100644
--- a/xen/include/public/arch-x86/cpufeatureset.h
+++ b/xen/include/public/arch-x86/cpufeatureset.h
@@ -135,7 +135,7 @@ XEN_CPUFEATURE(SSSE3, 1*32+ 9) /*A Supplemental
Streaming SIMD Extensio
XEN_CPUFEATURE(FMA, 1*32+12) /*A Fused Multiply Add */
XEN_CPUFEATURE(CX16, 1*32+13) /*A CMPXCHG16B */
XEN_CPUFEATURE(XTPR, 1*32+14) /* Send Task Priority Messages */
-XEN_CPUFEATURE(PDCM, 1*32+15) /* Perf/Debug Capability MSR */
+XEN_CPUFEATURE(PDCM, 1*32+15) /*S Perf/Debug Capability MSR */
XEN_CPUFEATURE(PCID, 1*32+17) /*H Process Context ID */
XEN_CPUFEATURE(DCA, 1*32+18) /* Direct Cache Access */
XEN_CPUFEATURE(SSE4_1, 1*32+19) /*A Streaming SIMD Extensions 4.1 */
--
2.36.0
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