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Date: Fri, 22 Oct 2021 17:23:23 +0100 From: James Clark <james.clark@....com> To: Leo Yan <leo.yan@...aro.org> Cc: Catalin Marinas <catalin.marinas@....com>, Will Deacon <will@...nel.org>, Mark Rutland <mark.rutland@....com>, Kees Cook <keescook@...omium.org>, Ard Biesheuvel <ardb@...nel.org>, Sami Tolvanen <samitolvanen@...gle.com>, Nicholas Piggin <npiggin@...il.com>, James Morse <james.morse@....com>, Marc Zyngier <maz@...nel.org>, Joey Gouly <joey.gouly@....com>, Peter Collingbourne <pcc@...gle.com>, Vincenzo Frascino <vincenzo.frascino@....com>, "Peter Zijlstra (Intel)" <peterz@...radead.org>, Stephane Eranian <eranian@...gle.com>, linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org Subject: Re: [RFCv1 4/4] perf: arm_spe: Dynamically switch PID tracing to contextidr On 22/10/2021 16:36, James Clark wrote: > > > On 21/10/2021 14:45, Leo Yan wrote: >> Now Arm64 provides API for enabling and disable PID tracing, Arm SPE >> driver invokes these functions to dynamically enable it during >> profiling when the program runs in root PID name space, and disable PID >> tracing when the perf event is stopped. >> >> Device drivers should not depend on CONFIG_PID_IN_CONTEXTIDR for PID >> tracing, so this patch uses the consistent condition for setting bit >> EL1_CX for PMSCR. > > Hi Leo, > > I've been testing this change, but I'm seeing something strange. Not sure > if it's a problem on my side or not yet. With this command: > > sudo ./perf record -vvv -e arm_spe//u -- taskset --cpu-list 1 bash -c ls > > I'm only seeing 0 values for context: > > sudo ./perf report -D | grep CONTEXT > > . 00038dce: 65 00 00 00 00 CONTEXT 0x0 el2 > . 00038e0e: 65 00 00 00 00 CONTEXT 0x0 el2 > > I added a printk to the function, and I see it print non zero values, although > there are some zero ones mixed in there too: > > diff --git a/arch/arm64/include/asm/mmu_context.h b/arch/arm64/include/asm/mmu_context.h > index 0c1669db19a1..8f0fb43a5fac 100644 > --- a/arch/arm64/include/asm/mmu_context.h > +++ b/arch/arm64/include/asm/mmu_context.h > @@ -33,7 +33,8 @@ static inline void contextidr_thread_switch(struct task_struct *next) > if (!static_branch_unlikely(&contextidr_in_use)) > return; > > - write_sysreg(task_pid_nr(next), contextidr_el1); > + printk("Set %d\n", task_pid_nr(next)); > + write_sysreg(task_pid_nr(next), contextidr_el2); > isb(); > } > > > Results in this: > > [ 53.257905] Set 77 > [ 53.257909] Set 0 > [ 53.258180] Set 77 > [ 53.258183] Set 0 > [ 53.258385] Set 309 > [ 53.258385] Set 172 > [ 53.258425] Set 77 > [ 53.258443] Set 990 > [ 53.258449] Set 77 > [ 53.258455] Set 990 > [ 53.258467] Set 310 > [ 53.258719] Set 7 > [ 53.258728] Set 77 > [ 53.258731] Set 0 > [ 53.258733] Set 0 > [ 53.258738] Set 7 > > > Without your patchset I don't get 0 values in the SPE trace anymore: > > . 0000050e: 65 b1 01 00 00 CONTEXT 0x1b1 el2 > . 0000054e: 65 b1 01 00 00 CONTEXT 0x1b1 el2 > . 0000058e: 65 ac 01 00 00 CONTEXT 0x1ac el2 > . 000005ce: 65 ac 01 00 00 CONTEXT 0x1ac el2 > Is it an issue with building with CONTEXTIDR disabled? Seems like this change results in context packets set to 0 when it's disabled rather than having the packets disabled like they used to be: zcat /proc/config.gz | grep CONTEXTIDR # CONFIG_PID_IN_CONTEXTIDR is not set sudo ./perf report -D | grep CONTEXT . 00045b4e: 65 00 00 00 00 CONTEXT 0x0 el2 When I build with CONFIG_PID_IN_CONTEXTIDR=y the contexts are non zero so it seems to be working that way. But ./perf record -e arm_spe//u -a does have context IDs even when CONFIG_PID_IN_CONTEXTIDR=n. So I'm still a bit confused.
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