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Message-ID: <ZtnbkxV8exv1F3H9@zx2c4.com>
Date: Thu, 5 Sep 2024 18:25:55 +0200
From: "Jason A. Donenfeld" <Jason@...c4.com>
To: Christophe Leroy <christophe.leroy@...roup.eu>
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
On Thu, Sep 05, 2024 at 06:13:29PM +0200, Jason A. Donenfeld wrote:
> > +/*
> > + * 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.
>
> 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.
>
> Can you figure out what's going on and send a fix, which I'll squash
> into this commit?
Also, FYI, I've verified that things do work on x86_64, loongarch64,
arm64, and arm64_be. It's just the ppc archs that are broken. So this
test _is_ a good one.
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