linux-kernel - Re: [PATCH v5 4/5] powerpc/vdso: Wire up getrandom() vDSO implementation on VDSO32

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Message-ID: <85c02620-e8b2-4c97-9905-685a9a4e556d@csgroup.eu>
Date: Thu, 5 Sep 2024 18:55:27 +0200
From: Christophe Leroy <christophe.leroy@...roup.eu>
To: "Jason A. Donenfeld" <Jason@...c4.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
 Steven Rostedt <rostedt@...dmis.org>, Masami Hiramatsu
 <mhiramat@...nel.org>, Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
 Michael Ellerman <mpe@...erman.id.au>, Nicholas Piggin <npiggin@...il.com>,
 Naveen N Rao <naveen@...nel.org>, Nathan Chancellor <nathan@...nel.org>,
 Nick Desaulniers <ndesaulniers@...gle.com>, Bill Wendling
 <morbo@...gle.com>, Justin Stitt <justinstitt@...gle.com>,
 Shuah Khan <shuah@...nel.org>, linux-kernel@...r.kernel.org,
 linuxppc-dev@...ts.ozlabs.org, linux-kselftest@...r.kernel.org,
 llvm@...ts.linux.dev, linux-fsdevel@...r.kernel.org, linux-mm@...ck.org,
 linux-trace-kernel@...r.kernel.org,
 Adhemerval Zanella <adhemerval.zanella@...aro.org>,
 Xi Ruoyao <xry111@...111.site>
Subject: Re: [PATCH v5 4/5] powerpc/vdso: Wire up getrandom() vDSO
 implementation on VDSO32

Le 05/09/2024 à 18:13, Jason A. Donenfeld a écrit :
>> +/*
>> + * The macro sets two stack frames, one for the caller and one for the callee
>> + * because there are no requirement for the caller to set a stack frame when
>> + * calling VDSO so it may have omitted to set one, especially on PPC64
>> + */
>> +
>> +.macro cvdso_call funct
>> +  .cfi_startproc
>> +	PPC_STLU	r1, -PPC_MIN_STKFRM(r1)
>> +  .cfi_adjust_cfa_offset PPC_MIN_STKFRM
>> +	mflr		r0
>> +	PPC_STLU	r1, -PPC_MIN_STKFRM(r1)
>> +  .cfi_adjust_cfa_offset PPC_MIN_STKFRM
>> +	PPC_STL		r0, PPC_MIN_STKFRM + PPC_LR_STKOFF(r1)
>> +  .cfi_rel_offset lr, PPC_MIN_STKFRM + PPC_LR_STKOFF
>> +	get_datapage	r8
>> +	addi		r8, r8, VDSO_RNG_DATA_OFFSET
>> +	bl		CFUNC(DOTSYM(\funct))
>> +	PPC_LL		r0, PPC_MIN_STKFRM + PPC_LR_STKOFF(r1)
>> +	cmpwi		r3, 0
>> +	mtlr		r0
>> +	addi		r1, r1, 2 * PPC_MIN_STKFRM
>> +  .cfi_restore lr
>> +  .cfi_def_cfa_offset 0
>> +	crclr		so
>> +	bgelr+
>> +	crset		so
>> +	neg		r3, r3
>> +	blr
>> +  .cfi_endproc
>> +.endm
> 
> You wrote in an earlier email that this worked with time namespaces, but
> in my testing that doesn't seem to be the case.

Did I write that ? I can't remember and neither can I remember testing 
it with time namespaces.

> 
>  From my test harness [1]:
> 
> Normal single thread
>     vdso: 25000000 times in 12.494133131 seconds
>     libc: 25000000 times in 69.594625188 seconds
> syscall: 25000000 times in 67.349243972 seconds
> Time namespace single thread
>     vdso: 25000000 times in 71.673057436 seconds
>     libc: 25000000 times in 71.712774121 seconds
> syscall: 25000000 times in 66.902318080 seconds
> 
> I'm seeing this on ppc, ppc64, and ppc64le.

What is the command to use to test with time namespace ?

> 
> Can you figure out what's going on and send a fix, which I'll squash
> into this commit?

Sure

> 
> Jason
> 
> [1] https://eur01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgit.zx2c4.com%2Flinux-rng%2Fcommit%2F%3Fh%3Djd%2Fvdso-test-harness&data=05%7C02%7Cchristophe.leroy%40csgroup.eu%7C59fa9061064945c73a1608dccdc5b51c%7C8b87af7d86474dc78df45f69a2011bb5%7C0%7C0%7C638611496253413014%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C0%7C%7C%7C&sdata=ZUJqhcnZL7SYkuXUIt9Nlo46sZj26VYW%2F8I%2BrBLRpBE%3D&reserved=0