[RFC PATCH 04/22] x86/msr: Adjust remote reads of IA32_[AM]PERF by the per-cpu host offset

Mingwei Zhang
2024-11-21T18:53:25Z

From: Jim Mattson <jmattson@google.com>

When reading IA32_APERF or IA32_MPERF remotely via /dev/cpu/*/msr,
account for any offset between the hardware MSR value and the true
host value. This ensures tools like turbostat get correct host values
even when the hardware MSRs contain guest values.

Signed-off-by: Jim Mattson <jmattson@google.com>
Reviewed-by: Mingwei Zhang <mizhang@google.com>
Signed-off-by: Mingwei Zhang <mizhang@google.com>
---
arch/x86/lib/msr-smp.c | 11 +++++++++++
1 file changed, 11 insertions(+)

diff --git a/arch/x86/lib/msr-smp.c b/arch/x86/lib/msr-smp.c
index acd463d887e1c..43c5d21e840fb 100644
--- a/arch/x86/lib/msr-smp.c
+++ b/arch/x86/lib/msr-smp.c
@@ -4,6 +4,15 @@
#include <linux/smp.h>
#include <linux/completion.h>
#include <asm/msr.h>
+#include <asm/topology.h>
+
+static void adjust_host_aperfmperf(u32 msr_no, struct msr *reg)
+{
+ if (msr_no == MSR_IA32_APERF)
+ reg->q += this_cpu_read(host_aperf_offset);
+ else if (msr_no == MSR_IA32_MPERF)
+ reg->q += this_cpu_read(host_mperf_offset);
+}

static void __rdmsr_on_cpu(void *info)
{
@@ -16,6 +25,7 @@ static void __rdmsr_on_cpu(void *info)
reg = &rv->reg;

rdmsr(rv->msr_no, reg->l, reg->h);
+ adjust_host_aperfmperf(rv->msr_no, reg);
}

static void __wrmsr_on_cpu(void *info)
@@ -154,6 +164,7 @@ static void __rdmsr_safe_on_cpu(void *info)
struct msr_info_completion *rv = info;

rv->msr.err = rdmsr_safe(rv->msr.msr_no, &rv->msr.reg.l, &rv->msr.reg.h);
+ adjust_host_aperfmperf(rv->msr.msr_no, &rv->msr.reg);
complete(&rv->done);
}

--
2.47.0.371.ga323438b13-goog