[PATCH v3] perf/x86/amd: Don't touch the Host-only bit inside the guest hypervisor

[PATCH v3] perf/x86/amd: Don't touch the Host-only bit inside the guest hypervisor

[Dongli Si]

From: Dongli Si <sidongli1997@gmail.com>

With nested virtualization on AMD Milan, if "perf record" is run in an
L1 hypervisor with an L2 guest, the following warning is emitted in
the L1 guest.

[] unchecked MSR access error: WRMSR to 0xc0010200 (tried to write 0x0000020000510076)
at rIP: 0xffffffff81003a50 (x86_pmu_enable_all+0x60/0x100)
[] Call Trace:
[]  <IRQ>
[]  ? x86_pmu_enable+0x146/0x300
[]  __perf_install_in_context+0x150/0x170

The AMD64_EVENTSEL_HOSTONLY bit is defined and used on the host (L0),
while the L1 hypervisor Performance Monitor Unit should avoid such use.

Fixes: 1018faa6cf23 ("perf/x86/kvm: Fix Host-Only/Guest-Only counting with SVM disabled")
Signed-off-by: Dongli Si <sidongli1997@gmail.com>
Tested-by: Liam Merwick <liam.merwick@oracle.com>
Reviewed-by: Liam Merwick <liam.merwick@oracle.com>
---
v3: Add Tested-by, Reviewed-by from Liam and improve description.
v2: https://lore.kernel.org/all/20220310183404.1291725-1-sidongli1997@gmail.com/
v1: https://lore.kernel.org/all/20220227132640.3-1-sidongli1997@gmail.com/

 arch/x86/events/amd/core.c        |  4 +++-
 arch/x86/include/asm/hypervisor.h | 10 ++++++++++
 2 files changed, 13 insertions(+), 1 deletion(-)

diff --git a/arch/x86/events/amd/core.c b/arch/x86/events/amd/core.c
index 9687a8aef01c..14cd079243a4 100644
--- a/arch/x86/events/amd/core.c
+++ b/arch/x86/events/amd/core.c
@@ -8,6 +8,7 @@
 #include <linux/jiffies.h>
 #include <asm/apicdef.h>
 #include <asm/nmi.h>
+#include <asm/hypervisor.h>
 
 #include "../perf_event.h"
 
@@ -1027,7 +1028,8 @@ void amd_pmu_enable_virt(void)
 {
 	struct cpu_hw_events *cpuc = this_cpu_ptr(&cpu_hw_events);
 
-	cpuc->perf_ctr_virt_mask = 0;
+	if (run_as_host())
+		cpuc->perf_ctr_virt_mask = 0;
 
 	/* Reload all events */
 	amd_pmu_disable_all();
diff --git a/arch/x86/include/asm/hypervisor.h b/arch/x86/include/asm/hypervisor.h
index e41cbf2ec41d..fcc66c23cc72 100644
--- a/arch/x86/include/asm/hypervisor.h
+++ b/arch/x86/include/asm/hypervisor.h
@@ -73,11 +73,21 @@ static inline bool hypervisor_is_type(enum x86_hypervisor_type type)
 {
 	return x86_hyper_type == type;
 }
+
+static inline bool run_as_host(void)
+{
+	return hypervisor_is_type(X86_HYPER_NATIVE);
+}
 #else
 static inline void init_hypervisor_platform(void) { }
 static inline bool hypervisor_is_type(enum x86_hypervisor_type type)
 {
 	return type == X86_HYPER_NATIVE;
 }
+
+static inline bool run_as_host(void)
+{
+	return true;
+}
 #endif /* CONFIG_HYPERVISOR_GUEST */
 #endif /* _ASM_X86_HYPERVISOR_H */
-- 
2.32.0

Re: [PATCH v3] perf/x86/amd: Don't touch the Host-only bit inside the guest hypervisor

[Borislav Petkov]

On Mon, Mar 14, 2022 at 12:22:54PM +0800, Dongli Si wrote:
> diff --git a/arch/x86/include/asm/hypervisor.h b/arch/x86/include/asm/hypervisor.h
> index e41cbf2ec41d..fcc66c23cc72 100644
> --- a/arch/x86/include/asm/hypervisor.h
> +++ b/arch/x86/include/asm/hypervisor.h
> @@ -73,11 +73,21 @@ static inline bool hypervisor_is_type(enum x86_hypervisor_type type)
>  {
>  	return x86_hyper_type == type;
>  }
> +
> +static inline bool run_as_host(void)
> +{
> +	return hypervisor_is_type(X86_HYPER_NATIVE);
> +}

What's the point of this "wrapper"?

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette

Re: [PATCH v3] perf/x86/amd: Don't touch the Host-only bit inside the guest hypervisor

[Dongli Si]

On 16/03/2022 18:29, Borislav Petkov wrote:
> What's the point of this "wrapper"?

Hi Borislav, this is just to more clearly test if the current kernel is
running directly on the host.

If this is redundant, I can remove this "wrapper" and resend the patch,
the v4 patch code will be the same as the v1 patch.
 
Thanks,
Dongli

Re: [PATCH v3] perf/x86/amd: Don't touch the Host-only bit inside the guest hypervisor

[Borislav Petkov]

On Fri, Mar 18, 2022 at 11:07:57AM +0800, Dongli Si wrote:
> Hi Borislav, this is just to more clearly test if the current kernel is
> running directly on the host.
> 
> If this is redundant, I can remove this "wrapper" and resend the patch,
> the v4 patch code will be the same as the v1 patch.

Yes please. Using

	hypervisor_is_type(X86_HYPER_NATIVE)

directly is a lot more descriptive than "run_as_host".

Thx.

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette