linux-kernel - Re: [PATCH v6 5/5] perf: Correct perf sampling with guest VMs

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Message-ID: <89b46b99-e9fc-4ce4-84b2-b24f565db8d5@linux.intel.com>
Date: Wed, 6 Nov 2024 15:38:25 -0500
From: "Liang, Kan" <kan.liang@...ux.intel.com>
To: Oliver Upton <oliver.upton@...ux.dev>
Cc: Colton Lewis <coltonlewis@...gle.com>, kvm@...r.kernel.org,
 Sean Christopherson <seanjc@...gle.com>,
 Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...hat.com>,
 Arnaldo Carvalho de Melo <acme@...nel.org>,
 Namhyung Kim <namhyung@...nel.org>, Mark Rutland <mark.rutland@....com>,
 Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
 Jiri Olsa <jolsa@...nel.org>, Ian Rogers <irogers@...gle.com>,
 Adrian Hunter <adrian.hunter@...el.com>, Will Deacon <will@...nel.org>,
 Russell King <linux@...linux.org.uk>,
 Catalin Marinas <catalin.marinas@....com>,
 Michael Ellerman <mpe@...erman.id.au>, Nicholas Piggin <npiggin@...il.com>,
 Christophe Leroy <christophe.leroy@...roup.eu>,
 Naveen N Rao <naveen@...nel.org>, Heiko Carstens <hca@...ux.ibm.com>,
 Vasily Gorbik <gor@...ux.ibm.com>, Alexander Gordeev
 <agordeev@...ux.ibm.com>, Christian Borntraeger <borntraeger@...ux.ibm.com>,
 Sven Schnelle <svens@...ux.ibm.com>, Thomas Gleixner <tglx@...utronix.de>,
 Borislav Petkov <bp@...en8.de>, Dave Hansen <dave.hansen@...ux.intel.com>,
 x86@...nel.org, "H . Peter Anvin" <hpa@...or.com>,
 linux-perf-users@...r.kernel.org, linux-kernel@...r.kernel.org,
 linux-arm-kernel@...ts.infradead.org, linuxppc-dev@...ts.ozlabs.org,
 linux-s390@...r.kernel.org
Subject: Re: [PATCH v6 5/5] perf: Correct perf sampling with guest VMs

On 2024-11-06 2:53 p.m., Oliver Upton wrote:
> On Wed, Nov 06, 2024 at 11:07:53AM -0500, Liang, Kan wrote:
>>> +#ifndef perf_arch_guest_misc_flags
>>> +static inline unsigned long perf_arch_guest_misc_flags(struct pt_regs *regs)
>>> +{
>>> +	unsigned long guest_state = perf_guest_state();
>>> +
>>> +	if (guest_state & PERF_GUEST_USER)
>>> +		return PERF_RECORD_MISC_GUEST_USER;
>>> +
>>> +	if (guest_state & PERF_GUEST_ACTIVE)
>>> +		return PERF_RECORD_MISC_GUEST_KERNEL;
>>
>> Is there by any chance to add a PERF_GUEST_KERNEL flag in KVM?
> 
> Why do we need another flag? As it stands today, the vCPU is either in
> user mode or kernel mode.
> 
>> The PERF_GUEST_ACTIVE flag check looks really confusing.
> 
> Perhaps instead:
> 
> static inline unsigned long perf_arch_guest_misc_flags(struct pt_regs *regs)
> {
> 	unsigned long guest_state = perf_guest_state();
> 
> 	if (!(guest_state & PERF_GUEST_ACTIVE))
> 		return 0;
> 
> 	return (guest_state & PERF_GUEST_USER) ? PERF_RECORD_MISC_GUEST_USER :
> 						 PERF_RECORD_MISC_GUEST_KERNEL;
> }

Yes, this one is much clear.

Can a similar change be done for the x86 perf_arch_guest_misc_flags() in
the previous patch?

Thanks,
Kan