[PATCH v4 0/5] KVM: x86: Intel LBR related perf cleanups

[PATCH v4 0/5] KVM: x86: Intel LBR related perf cleanups

[Sean Christopherson]

Fix a bug where KVM incorrectly advertises PMU_CAP_LBR_FMT to userspace if
perf has disabled LBRs, e.g. because probing one or more LBR MSRs during
setup hit a #GP.

The non-KVM patches remove unnecessary stubs and unreachable error paths,
which allows for a cleaner fix for said bug (backporting is unlikely to be
necessary/requested).

v4
 - Make vmx_get_perf_capabilities() non-inline to avoid references to
   x86_perf_get_lbr() when CPU_SUP_INTEL=n. [kernel test robot]

v3:
 - https://lore.kernel.org/all/20220831000051.4015031-1-seanjc@google.com
 - Drop patches for bug #1 (already merged).
 - Drop misguided "clean up the capability check" patch. [Like]

v2:
 - https://lore.kernel.org/all/20220803192658.860033-1-seanjc@google.com
 - Add patches to fix bug #2. [Like]
 - Add a patch to clean up the capability check.
 - Tweak the changelog for the PMU refresh bug fix to call out that
   KVM should disallow changing feature MSRs after KVM_RUN. [Like]

v1: https://lore.kernel.org/all/20220727233424.2968356-1-seanjc@google.com

Sean Christopherson (5):
  perf/x86/core: Remove unnecessary stubs provided for KVM-only helpers
  perf/x86/core: Drop the unnecessary return value from
    x86_perf_get_lbr()
  KVM: VMX: Move vmx_get_perf_capabilities() definition to vmx.c
  KVM: VMX: Fold vmx_supported_debugctl() into vcpu_supported_debugctl()
  KVM: VMX: Advertise PMU LBRs if and only if perf supports LBRs

 arch/x86/events/intel/lbr.c       |  6 +---
 arch/x86/include/asm/perf_event.h | 55 ++++++++-----------------------
 arch/x86/kvm/vmx/capabilities.h   | 39 ++--------------------
 arch/x86/kvm/vmx/vmx.c            | 37 ++++++++++++++++++---
 4 files changed, 49 insertions(+), 88 deletions(-)


base-commit: 372d07084593dc7a399bf9bee815711b1fb1bcf2
-- 
2.37.2.789.g6183377224-goog

[PATCH v4 1/5] perf/x86/core: Remove unnecessary stubs provided for KVM-only helpers

[Sean Christopherson]

Remove CONFIG_PERF_EVENT=n stubs for functions that are effectively
KVM-only.  KVM selects PERF_EVENT and will never consume the stubs.
Dropping the unnecessary stubs will allow simplifying x86_perf_get_lbr()
by getting rid of the impossible-to-hit error path (which KVM doesn't
even check).

Opportunstically reorganize the declarations to collapse multiple
CONFIG_PERF_EVENTS #ifdefs.

Signed-off-by: Sean Christopherson <seanjc@google.com>
---
 arch/x86/include/asm/perf_event.h | 53 ++++++++-----------------------
 1 file changed, 13 insertions(+), 40 deletions(-)

diff --git a/arch/x86/include/asm/perf_event.h b/arch/x86/include/asm/perf_event.h
index f6fc8dd51ef4..f839eb55f298 100644
--- a/arch/x86/include/asm/perf_event.h
+++ b/arch/x86/include/asm/perf_event.h
@@ -525,46 +525,18 @@ extern u64 perf_get_hw_event_config(int hw_event);
 extern void perf_check_microcode(void);
 extern void perf_clear_dirty_counters(void);
 extern int x86_perf_rdpmc_index(struct perf_event *event);
-#else
-static inline void perf_get_x86_pmu_capability(struct x86_pmu_capability *cap)
-{
-	memset(cap, 0, sizeof(*cap));
-}
 
-static inline u64 perf_get_hw_event_config(int hw_event)
-{
-	return 0;
-}
-
-static inline void perf_events_lapic_init(void)	{ }
-static inline void perf_check_microcode(void) { }
-#endif
-
-#if defined(CONFIG_PERF_EVENTS) && defined(CONFIG_CPU_SUP_INTEL)
+#ifdef CONFIG_CPU_SUP_INTEL
 extern struct perf_guest_switch_msr *perf_guest_get_msrs(int *nr, void *data);
 extern int x86_perf_get_lbr(struct x86_pmu_lbr *lbr);
-#else
-struct perf_guest_switch_msr *perf_guest_get_msrs(int *nr, void *data);
-static inline int x86_perf_get_lbr(struct x86_pmu_lbr *lbr)
-{
-	return -1;
-}
-#endif
+extern void intel_pt_handle_vmx(int on);
+#endif /* CONFIG_CPU_SUP_INTEL */
 
-#ifdef CONFIG_CPU_SUP_INTEL
- extern void intel_pt_handle_vmx(int on);
-#else
-static inline void intel_pt_handle_vmx(int on)
-{
+#ifdef CONFIG_CPU_SUP_AMD
+extern void amd_pmu_enable_virt(void);
+extern void amd_pmu_disable_virt(void);
 
-}
-#endif
-
-#if defined(CONFIG_PERF_EVENTS) && defined(CONFIG_CPU_SUP_AMD)
- extern void amd_pmu_enable_virt(void);
- extern void amd_pmu_disable_virt(void);
-
-#if defined(CONFIG_PERF_EVENTS_AMD_BRS)
+#ifdef CONFIG_PERF_EVENTS_AMD_BRS
 
 #define PERF_NEEDS_LOPWR_CB 1
 
@@ -582,12 +554,13 @@ static inline void perf_lopwr_cb(bool lopwr_in)
 	static_call_mod(perf_lopwr_cb)(lopwr_in);
 }
 
-#endif /* PERF_NEEDS_LOPWR_CB */
+#endif /* CONFIG_PERF_EVENTS_AMD_BRS */
+#endif /* CONFIG_CPU_SUP_AMD */
 
-#else
- static inline void amd_pmu_enable_virt(void) { }
- static inline void amd_pmu_disable_virt(void) { }
-#endif
+#else  /* !CONFIG_PERF_EVENTS */
+static inline void perf_events_lapic_init(void)	{ }
+static inline void perf_check_microcode(void) { }
+#endif /* CONFIG_PERF_EVENTS */
 
 #define arch_perf_out_copy_user copy_from_user_nmi
 
-- 
2.37.2.789.g6183377224-goog

Re: [PATCH v4 1/5] perf/x86/core: Remove unnecessary stubs provided for KVM-only helpers

[kernel test robot]

Hi Sean,

I love your patch! Perhaps something to improve:

[auto build test WARNING on 372d07084593dc7a399bf9bee815711b1fb1bcf2]

url:    https://github.com/intel-lab-lkp/linux/commits/Sean-Christopherson/KVM-x86-Intel-LBR-related-perf-cleanups/20220902-013352
base:   372d07084593dc7a399bf9bee815711b1fb1bcf2
config: i386-randconfig-m021 (https://download.01.org/0day-ci/archive/20220902/202209021042.UcDPO3lL-lkp@intel.com/config)
compiler: gcc-11 (Debian 11.3.0-5) 11.3.0
reproduce (this is a W=1 build):
        # https://github.com/intel-lab-lkp/linux/commit/b1f1d2f5eb44253f5d059757c03e7fd413b2e306
        git remote add linux-review https://github.com/intel-lab-lkp/linux
        git fetch --no-tags linux-review Sean-Christopherson/KVM-x86-Intel-LBR-related-perf-cleanups/20220902-013352
        git checkout b1f1d2f5eb44253f5d059757c03e7fd413b2e306
        # save the config file
        mkdir build_dir && cp config build_dir/.config
        make W=1 O=build_dir ARCH=i386 SHELL=/bin/bash arch/x86/events/

If you fix the issue, kindly add following tag where applicable
Reported-by: kernel test robot <lkp@intel.com>

All warnings (new ones prefixed by >>):

>> arch/x86/events/core.c:696:31: warning: no previous prototype for 'perf_guest_get_msrs' [-Wmissing-prototypes]
     696 | struct perf_guest_switch_msr *perf_guest_get_msrs(int *nr, void *data)
         |                               ^~~~~~~~~~~~~~~~~~~


vim +/perf_guest_get_msrs +696 arch/x86/events/core.c

f87ad35d37fa54 arch/x86/kernel/cpu/perf_counter.c Jaswinder Singh Rajput 2009-02-27  695  
39a4d779546a99 arch/x86/events/core.c             Like Xu                2022-04-11 @696  struct perf_guest_switch_msr *perf_guest_get_msrs(int *nr, void *data)
abd562df94d19d arch/x86/events/core.c             Like Xu                2021-01-25  697  {
39a4d779546a99 arch/x86/events/core.c             Like Xu                2022-04-11  698  	return static_call(x86_pmu_guest_get_msrs)(nr, data);
abd562df94d19d arch/x86/events/core.c             Like Xu                2021-01-25  699  }
abd562df94d19d arch/x86/events/core.c             Like Xu                2021-01-25  700  EXPORT_SYMBOL_GPL(perf_guest_get_msrs);
abd562df94d19d arch/x86/events/core.c             Like Xu                2021-01-25  701  

-- 
0-DAY CI Kernel Test Service
https://01.org/lkp

Re: [PATCH v4 1/5] perf/x86/core: Remove unnecessary stubs provided for KVM-only helpers

[kernel test robot]

Hi Sean,

I love your patch! Perhaps something to improve:

[auto build test WARNING on 372d07084593dc7a399bf9bee815711b1fb1bcf2]

url:    https://github.com/intel-lab-lkp/linux/commits/Sean-Christopherson/KVM-x86-Intel-LBR-related-perf-cleanups/20220902-013352
base:   372d07084593dc7a399bf9bee815711b1fb1bcf2
config: x86_64-randconfig-a012 (https://download.01.org/0day-ci/archive/20220902/202209021033.bPC3ttgM-lkp@intel.com/config)
compiler: clang version 14.0.6 (https://github.com/llvm/llvm-project f28c006a5895fc0e329fe15fead81e37457cb1d1)
reproduce (this is a W=1 build):
        wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
        chmod +x ~/bin/make.cross
        # https://github.com/intel-lab-lkp/linux/commit/b1f1d2f5eb44253f5d059757c03e7fd413b2e306
        git remote add linux-review https://github.com/intel-lab-lkp/linux
        git fetch --no-tags linux-review Sean-Christopherson/KVM-x86-Intel-LBR-related-perf-cleanups/20220902-013352
        git checkout b1f1d2f5eb44253f5d059757c03e7fd413b2e306
        # save the config file
        mkdir build_dir && cp config build_dir/.config
        COMPILER_INSTALL_PATH=$HOME/0day COMPILER=clang make.cross W=1 O=build_dir ARCH=x86_64 SHELL=/bin/bash arch/x86/events/

If you fix the issue, kindly add following tag where applicable
Reported-by: kernel test robot <lkp@intel.com>

All warnings (new ones prefixed by >>):

>> arch/x86/events/core.c:696:31: warning: no previous prototype for function 'perf_guest_get_msrs' [-Wmissing-prototypes]
   struct perf_guest_switch_msr *perf_guest_get_msrs(int *nr, void *data)
                                 ^
   arch/x86/events/core.c:696:1: note: declare 'static' if the function is not intended to be used outside of this translation unit
   struct perf_guest_switch_msr *perf_guest_get_msrs(int *nr, void *data)
   ^
   static 
   1 warning generated.


vim +/perf_guest_get_msrs +696 arch/x86/events/core.c

f87ad35d37fa54 arch/x86/kernel/cpu/perf_counter.c Jaswinder Singh Rajput 2009-02-27  695  
39a4d779546a99 arch/x86/events/core.c             Like Xu                2022-04-11 @696  struct perf_guest_switch_msr *perf_guest_get_msrs(int *nr, void *data)
abd562df94d19d arch/x86/events/core.c             Like Xu                2021-01-25  697  {
39a4d779546a99 arch/x86/events/core.c             Like Xu                2022-04-11  698  	return static_call(x86_pmu_guest_get_msrs)(nr, data);
abd562df94d19d arch/x86/events/core.c             Like Xu                2021-01-25  699  }
abd562df94d19d arch/x86/events/core.c             Like Xu                2021-01-25  700  EXPORT_SYMBOL_GPL(perf_guest_get_msrs);
abd562df94d19d arch/x86/events/core.c             Like Xu                2021-01-25  701  

-- 
0-DAY CI Kernel Test Service
https://01.org/lkp

Re: [PATCH v4 1/5] perf/x86/core: Remove unnecessary stubs provided for KVM-only helpers

[kernel test robot]

Hi Sean,

I love your patch! Perhaps something to improve:

[auto build test WARNING on 372d07084593dc7a399bf9bee815711b1fb1bcf2]

url:    https://github.com/intel-lab-lkp/linux/commits/Sean-Christopherson/KVM-x86-Intel-LBR-related-perf-cleanups/20220902-013352
base:   372d07084593dc7a399bf9bee815711b1fb1bcf2
config: x86_64-randconfig-a001 (https://download.01.org/0day-ci/archive/20220902/202209021001.ubosxpCd-lkp@intel.com/config)
compiler: clang version 14.0.6 (https://github.com/llvm/llvm-project f28c006a5895fc0e329fe15fead81e37457cb1d1)
reproduce (this is a W=1 build):
        wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
        chmod +x ~/bin/make.cross
        # https://github.com/intel-lab-lkp/linux/commit/b1f1d2f5eb44253f5d059757c03e7fd413b2e306
        git remote add linux-review https://github.com/intel-lab-lkp/linux
        git fetch --no-tags linux-review Sean-Christopherson/KVM-x86-Intel-LBR-related-perf-cleanups/20220902-013352
        git checkout b1f1d2f5eb44253f5d059757c03e7fd413b2e306
        # save the config file
        mkdir build_dir && cp config build_dir/.config
        COMPILER_INSTALL_PATH=$HOME/0day COMPILER=clang make.cross W=1 O=build_dir ARCH=x86_64 SHELL=/bin/bash arch/x86/events/

If you fix the issue, kindly add following tag where applicable
Reported-by: kernel test robot <lkp@intel.com>

All warnings (new ones prefixed by >>):

>> arch/x86/events/core.c:696:31: warning: no previous prototype for function 'perf_guest_get_msrs' [-Wmissing-prototypes]
   struct perf_guest_switch_msr *perf_guest_get_msrs(int *nr, void *data)
                                 ^
   arch/x86/events/core.c:696:1: note: declare 'static' if the function is not intended to be used outside of this translation unit
   struct perf_guest_switch_msr *perf_guest_get_msrs(int *nr, void *data)
   ^
   static 
   1 warning generated.


vim +/perf_guest_get_msrs +696 arch/x86/events/core.c

f87ad35d37fa54 arch/x86/kernel/cpu/perf_counter.c Jaswinder Singh Rajput 2009-02-27  695  
39a4d779546a99 arch/x86/events/core.c             Like Xu                2022-04-11 @696  struct perf_guest_switch_msr *perf_guest_get_msrs(int *nr, void *data)
abd562df94d19d arch/x86/events/core.c             Like Xu                2021-01-25  697  {
39a4d779546a99 arch/x86/events/core.c             Like Xu                2022-04-11  698  	return static_call(x86_pmu_guest_get_msrs)(nr, data);
abd562df94d19d arch/x86/events/core.c             Like Xu                2021-01-25  699  }
abd562df94d19d arch/x86/events/core.c             Like Xu                2021-01-25  700  EXPORT_SYMBOL_GPL(perf_guest_get_msrs);
abd562df94d19d arch/x86/events/core.c             Like Xu                2021-01-25  701  

-- 
0-DAY CI Kernel Test Service
https://01.org/lkp

[PATCH v4 2/5] perf/x86/core: Drop the unnecessary return value from x86_perf_get_lbr()

[Sean Christopherson]

Drop the return value from x86_perf_get_lbr() now that there's no stub,
i.e. now that success is guaranteed (which is a bit of a lie since
success was always guaranteed, it's just more obvious now).

Signed-off-by: Sean Christopherson <seanjc@google.com>
---
 arch/x86/events/intel/lbr.c       | 6 +-----
 arch/x86/include/asm/perf_event.h | 2 +-
 2 files changed, 2 insertions(+), 6 deletions(-)

diff --git a/arch/x86/events/intel/lbr.c b/arch/x86/events/intel/lbr.c
index 4f70fb6c2c1e..b8ad31c52cf0 100644
--- a/arch/x86/events/intel/lbr.c
+++ b/arch/x86/events/intel/lbr.c
@@ -1868,10 +1868,8 @@ void __init intel_pmu_arch_lbr_init(void)
  * x86_perf_get_lbr - get the LBR records information
  *
  * @lbr: the caller's memory to store the LBR records information
- *
- * Returns: 0 indicates the LBR info has been successfully obtained
  */
-int x86_perf_get_lbr(struct x86_pmu_lbr *lbr)
+void x86_perf_get_lbr(struct x86_pmu_lbr *lbr)
 {
 	int lbr_fmt = x86_pmu.intel_cap.lbr_format;
 
@@ -1879,8 +1877,6 @@ int x86_perf_get_lbr(struct x86_pmu_lbr *lbr)
 	lbr->from = x86_pmu.lbr_from;
 	lbr->to = x86_pmu.lbr_to;
 	lbr->info = (lbr_fmt == LBR_FORMAT_INFO) ? x86_pmu.lbr_info : 0;
-
-	return 0;
 }
 EXPORT_SYMBOL_GPL(x86_perf_get_lbr);
 
diff --git a/arch/x86/include/asm/perf_event.h b/arch/x86/include/asm/perf_event.h
index f839eb55f298..f6d9230cdfab 100644
--- a/arch/x86/include/asm/perf_event.h
+++ b/arch/x86/include/asm/perf_event.h
@@ -528,7 +528,7 @@ extern int x86_perf_rdpmc_index(struct perf_event *event);
 
 #ifdef CONFIG_CPU_SUP_INTEL
 extern struct perf_guest_switch_msr *perf_guest_get_msrs(int *nr, void *data);
-extern int x86_perf_get_lbr(struct x86_pmu_lbr *lbr);
+extern void x86_perf_get_lbr(struct x86_pmu_lbr *lbr);
 extern void intel_pt_handle_vmx(int on);
 #endif /* CONFIG_CPU_SUP_INTEL */
 
-- 
2.37.2.789.g6183377224-goog

[PATCH v4 3/5] KVM: VMX: Move vmx_get_perf_capabilities() definition to vmx.c

[Sean Christopherson]

Move vmx_get_perf_capabilities() to vmx.c as a non-inline function so
that it can safely reference x86_perf_get_lbr(), which is available iff
CPU_SUP_INTEL=y, i.e. only if kvm_intel is being built.  The helper is
non-trivial and isn't used in any paths that are performance critical,
i.e. doesn't need to be inlined.

No functional change intended.

Signed-off-by: Sean Christopherson <seanjc@google.com>
---
 arch/x86/kvm/vmx/capabilities.h | 24 ++----------------------
 arch/x86/kvm/vmx/vmx.c          | 22 ++++++++++++++++++++++
 2 files changed, 24 insertions(+), 22 deletions(-)

diff --git a/arch/x86/kvm/vmx/capabilities.h b/arch/x86/kvm/vmx/capabilities.h
index c5e5dfef69c7..23dca5ebae16 100644
--- a/arch/x86/kvm/vmx/capabilities.h
+++ b/arch/x86/kvm/vmx/capabilities.h
@@ -75,6 +75,8 @@ struct vmx_capability {
 };
 extern struct vmx_capability vmx_capability;
 
+u64 vmx_get_perf_capabilities(void);
+
 static inline bool cpu_has_vmx_basic_inout(void)
 {
 	return	(((u64)vmcs_config.basic_cap << 32) & VMX_BASIC_INOUT);
@@ -401,28 +403,6 @@ static inline bool vmx_pebs_supported(void)
 	return boot_cpu_has(X86_FEATURE_PEBS) && kvm_pmu_cap.pebs_ept;
 }
 
-static inline u64 vmx_get_perf_capabilities(void)
-{
-	u64 perf_cap = PMU_CAP_FW_WRITES;
-	u64 host_perf_cap = 0;
-
-	if (!enable_pmu)
-		return 0;
-
-	if (boot_cpu_has(X86_FEATURE_PDCM))
-		rdmsrl(MSR_IA32_PERF_CAPABILITIES, host_perf_cap);
-
-	perf_cap |= host_perf_cap & PMU_CAP_LBR_FMT;
-
-	if (vmx_pebs_supported()) {
-		perf_cap |= host_perf_cap & PERF_CAP_PEBS_MASK;
-		if ((perf_cap & PERF_CAP_PEBS_FORMAT) < 4)
-			perf_cap &= ~PERF_CAP_PEBS_BASELINE;
-	}
-
-	return perf_cap;
-}
-
 static inline u64 vmx_supported_debugctl(void)
 {
 	u64 debugctl = 0;
diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index c9b49a09e6b5..657fa9908bf9 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -1826,6 +1826,28 @@ static inline bool vmx_feature_control_msr_valid(struct kvm_vcpu *vcpu,
 	return !(val & ~valid_bits);
 }
 
+u64 vmx_get_perf_capabilities(void)
+{
+	u64 perf_cap = PMU_CAP_FW_WRITES;
+	u64 host_perf_cap = 0;
+
+	if (!enable_pmu)
+		return 0;
+
+	if (boot_cpu_has(X86_FEATURE_PDCM))
+		rdmsrl(MSR_IA32_PERF_CAPABILITIES, host_perf_cap);
+
+	perf_cap |= host_perf_cap & PMU_CAP_LBR_FMT;
+
+	if (vmx_pebs_supported()) {
+		perf_cap |= host_perf_cap & PERF_CAP_PEBS_MASK;
+		if ((perf_cap & PERF_CAP_PEBS_FORMAT) < 4)
+			perf_cap &= ~PERF_CAP_PEBS_BASELINE;
+	}
+
+	return perf_cap;
+}
+
 static int vmx_get_msr_feature(struct kvm_msr_entry *msr)
 {
 	switch (msr->index) {
-- 
2.37.2.789.g6183377224-goog

[PATCH v4 4/5] KVM: VMX: Fold vmx_supported_debugctl() into vcpu_supported_debugctl()

[Sean Christopherson]

Fold vmx_supported_debugctl() into vcpu_supported_debugctl(), its only
caller.  Setting bits only to clear them a few instructions later is
rather silly, and splitting the logic makes things seem more complicated
than they actually are.

Opportunistically drop DEBUGCTLMSR_LBR_MASK now that there's a single
reference to the pair of bits.  The extra layer of indirection provides
no meaningful value and makes it unnecessarily tedious to understand
what KVM is doing.

No functional change.

Signed-off-by: Sean Christopherson <seanjc@google.com>
---
 arch/x86/kvm/vmx/capabilities.h | 15 ---------------
 arch/x86/kvm/vmx/vmx.c          | 12 +++++++-----
 2 files changed, 7 insertions(+), 20 deletions(-)

diff --git a/arch/x86/kvm/vmx/capabilities.h b/arch/x86/kvm/vmx/capabilities.h
index 23dca5ebae16..189a64a6e139 100644
--- a/arch/x86/kvm/vmx/capabilities.h
+++ b/arch/x86/kvm/vmx/capabilities.h
@@ -24,8 +24,6 @@ extern int __read_mostly pt_mode;
 #define PMU_CAP_FW_WRITES	(1ULL << 13)
 #define PMU_CAP_LBR_FMT		0x3f
 
-#define DEBUGCTLMSR_LBR_MASK		(DEBUGCTLMSR_LBR | DEBUGCTLMSR_FREEZE_LBRS_ON_PMI)
-
 struct nested_vmx_msrs {
 	/*
 	 * We only store the "true" versions of the VMX capability MSRs. We
@@ -403,19 +401,6 @@ static inline bool vmx_pebs_supported(void)
 	return boot_cpu_has(X86_FEATURE_PEBS) && kvm_pmu_cap.pebs_ept;
 }
 
-static inline u64 vmx_supported_debugctl(void)
-{
-	u64 debugctl = 0;
-
-	if (boot_cpu_has(X86_FEATURE_BUS_LOCK_DETECT))
-		debugctl |= DEBUGCTLMSR_BUS_LOCK_DETECT;
-
-	if (vmx_get_perf_capabilities() & PMU_CAP_LBR_FMT)
-		debugctl |= DEBUGCTLMSR_LBR_MASK;
-
-	return debugctl;
-}
-
 static inline bool cpu_has_notify_vmexit(void)
 {
 	return vmcs_config.cpu_based_2nd_exec_ctrl &
diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index 657fa9908bf9..a5e3c1e6aa2b 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -2030,13 +2030,15 @@ static u64 nested_vmx_truncate_sysenter_addr(struct kvm_vcpu *vcpu,
 
 static u64 vcpu_supported_debugctl(struct kvm_vcpu *vcpu)
 {
-	u64 debugctl = vmx_supported_debugctl();
+	u64 debugctl = 0;
 
-	if (!intel_pmu_lbr_is_enabled(vcpu))
-		debugctl &= ~DEBUGCTLMSR_LBR_MASK;
+	if (boot_cpu_has(X86_FEATURE_BUS_LOCK_DETECT) &&
+	    guest_cpuid_has(vcpu, X86_FEATURE_BUS_LOCK_DETECT))
+		debugctl |= DEBUGCTLMSR_BUS_LOCK_DETECT;
 
-	if (!guest_cpuid_has(vcpu, X86_FEATURE_BUS_LOCK_DETECT))
-		debugctl &= ~DEBUGCTLMSR_BUS_LOCK_DETECT;
+	if ((vmx_get_perf_capabilities() & PMU_CAP_LBR_FMT) &&
+	    intel_pmu_lbr_is_enabled(vcpu))
+		debugctl |= DEBUGCTLMSR_LBR | DEBUGCTLMSR_FREEZE_LBRS_ON_PMI;
 
 	return debugctl;
 }
-- 
2.37.2.789.g6183377224-goog

[PATCH v4 5/5] KVM: VMX: Advertise PMU LBRs if and only if perf supports LBRs

[Sean Christopherson]

Advertise LBR support to userspace via MSR_IA32_PERF_CAPABILITIES if and
only if perf fully supports LBRs.  Perf may disable LBRs (by zeroing the
number of LBRs) even on platforms the allegedly support LBRs, e.g. if
probing any LBR MSRs during setup fails.

Fixes: be635e34c284 ("KVM: vmx/pmu: Expose LBR_FMT in the MSR_IA32_PERF_CAPABILITIES")
Reported-by: Like Xu <like.xu.linux@gmail.com>
Signed-off-by: Sean Christopherson <seanjc@google.com>
---
 arch/x86/kvm/vmx/vmx.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index a5e3c1e6aa2b..8e237268ac10 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -1829,6 +1829,7 @@ static inline bool vmx_feature_control_msr_valid(struct kvm_vcpu *vcpu,
 u64 vmx_get_perf_capabilities(void)
 {
 	u64 perf_cap = PMU_CAP_FW_WRITES;
+	struct x86_pmu_lbr lbr;
 	u64 host_perf_cap = 0;
 
 	if (!enable_pmu)
@@ -1837,7 +1838,9 @@ u64 vmx_get_perf_capabilities(void)
 	if (boot_cpu_has(X86_FEATURE_PDCM))
 		rdmsrl(MSR_IA32_PERF_CAPABILITIES, host_perf_cap);
 
-	perf_cap |= host_perf_cap & PMU_CAP_LBR_FMT;
+	x86_perf_get_lbr(&lbr);
+	if (lbr.nr)
+		perf_cap |= host_perf_cap & PMU_CAP_LBR_FMT;
 
 	if (vmx_pebs_supported()) {
 		perf_cap |= host_perf_cap & PERF_CAP_PEBS_MASK;
-- 
2.37.2.789.g6183377224-goog

Re: [PATCH v4 0/5] KVM: x86: Intel LBR related perf cleanups

[Peter Zijlstra]

On Thu, Sep 01, 2022 at 05:32:53PM +0000, Sean Christopherson wrote:

> Sean Christopherson (5):
>   perf/x86/core: Remove unnecessary stubs provided for KVM-only helpers
>   perf/x86/core: Drop the unnecessary return value from
>     x86_perf_get_lbr()
>   KVM: VMX: Move vmx_get_perf_capabilities() definition to vmx.c
>   KVM: VMX: Fold vmx_supported_debugctl() into vcpu_supported_debugctl()
>   KVM: VMX: Advertise PMU LBRs if and only if perf supports LBRs

These look good to me; how do you want this routed, if through the KVM
tree:

Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>

Re: [PATCH v4 0/5] KVM: x86: Intel LBR related perf cleanups

[Sean Christopherson]

On Thu, Sep 08, 2022, Peter Zijlstra wrote:
> On Thu, Sep 01, 2022 at 05:32:53PM +0000, Sean Christopherson wrote:
> 
> > Sean Christopherson (5):
> >   perf/x86/core: Remove unnecessary stubs provided for KVM-only helpers
> >   perf/x86/core: Drop the unnecessary return value from
> >     x86_perf_get_lbr()
> >   KVM: VMX: Move vmx_get_perf_capabilities() definition to vmx.c
> >   KVM: VMX: Fold vmx_supported_debugctl() into vcpu_supported_debugctl()
> >   KVM: VMX: Advertise PMU LBRs if and only if perf supports LBRs
> 
> These look good to me; how do you want this routed, if through the KVM
> tree:
> 
> Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>

Thanks!  If you don't anticipate conflicts in the perf headers, I'll take 'em
through KVM, patch 01 introduced a new warning that I need to resolve (hopefully
it doesn't throw a wrench into things).

Re: [PATCH v4 0/5] KVM: x86: Intel LBR related perf cleanups

[Sean Christopherson]

On Sat, Sep 17, 2022, Sean Christopherson wrote:
> On Thu, Sep 08, 2022, Peter Zijlstra wrote:
> > On Thu, Sep 01, 2022 at 05:32:53PM +0000, Sean Christopherson wrote:
> > 
> > > Sean Christopherson (5):
> > >   perf/x86/core: Remove unnecessary stubs provided for KVM-only helpers
> > >   perf/x86/core: Drop the unnecessary return value from
> > >     x86_perf_get_lbr()
> > >   KVM: VMX: Move vmx_get_perf_capabilities() definition to vmx.c
> > >   KVM: VMX: Fold vmx_supported_debugctl() into vcpu_supported_debugctl()
> > >   KVM: VMX: Advertise PMU LBRs if and only if perf supports LBRs
> > 
> > These look good to me; how do you want this routed, if through the KVM
> > tree:
> > 
> > Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
> 
> Thanks!  If you don't anticipate conflicts in the perf headers, I'll take 'em
> through KVM, patch 01 introduced a new warning that I need to resolve (hopefully
> it doesn't throw a wrench into things).

Rats, patch 01 is flat out wrong.  The stubs for Intel and AMD are necessary
because KVM_{AMD,INTEL} don't strictly require CPU_SUP_{AMD/INTEL}.  KVM_AMD
doesn't have any CPU_SUP_* requirement (which probably should be fixed), and
KVM_INTEL effectively require INTEL || CENTAUR || ZHAOXIN.

x86_perf_get_lbr() can still be cleaned up to fix KVM's benign bug of not checking
the result by zeroing the structure when LBRs are unsupported.

v5 incoming...