Re: [PATCH v14 00/39] arm64/sme: Initial support for the Scalable Matrix Extension

From: Mark Brown <broonie@kernel.org>
To: Qian Cai <quic_qiancai@quicinc.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>,
	Will Deacon <will@kernel.org>, Marc Zyngier <maz@kernel.org>,
	Shuah Khan <skhan@linuxfoundation.org>,
	Shuah Khan <shuah@kernel.org>,
	Basant Kumar Dwivedi <Basant.KumarDwivedi@arm.com>,
	Luis Machado <luis.machado@arm.com>,
	Szabolcs Nagy <szabolcs.nagy@arm.com>,
	linux-arm-kernel@lists.infradead.org,
	linux-kselftest@vger.kernel.org,
	Alan Hayward <alan.hayward@arm.com>,
	kvmarm@lists.cs.columbia.edu,
	Salil Akerkar <Salil.Akerkar@arm.com>,
	Luca Salabrino <luca.scalabrino@arm.com>
Subject: Re: [PATCH v14 00/39] arm64/sme: Initial support for the Scalable Matrix Extension
Date: Wed, 4 May 2022 00:52:20 +0100	[thread overview]
Message-ID: <YnHANG5cM0CS9ffm@sirena.org.uk> (raw)
In-Reply-To: <YnGrbEt3oBBTly7u@qian>


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On Tue, May 03, 2022 at 06:23:40PM -0400, Qian Cai wrote:
> On Tue, Apr 19, 2022 at 12:22:08PM +0100, Mark Brown wrote:
> > This series provides initial support for the ARMv9 Scalable Matrix
> > Extension (SME).  SME takes the approach used for vectors in SVE and
> > extends this to provide architectural support for matrix operations.  A
> > more detailed overview can be found in [1].
> 
> Set CONFIG_ARM64_SME=n fixed a warning while running libhugetlbfs tests.
> 
>         /*
>          * There are several places where we assume that the order value is sane
>          * so bail out early if the request is out of bound.
>          */
>         if (unlikely(order >= MAX_ORDER)) {
>                 WARN_ON_ONCE(!(gfp & __GFP_NOWARN));
>                 return NULL;
>         }

Ugh, right.  These variable sized register sets really don't map
entirely cleanly onto the ptrace interface but now you point it
out what the code has there is going to give a rather larger
number than is sensible.  Not fully checked but does the below
fix things?

Thanks for your testing with this stuff, it's been really
helpful.

diff --git a/arch/arm64/kernel/ptrace.c b/arch/arm64/kernel/ptrace.c
index 47d8a7472171..08c1cb43cf33 100644
--- a/arch/arm64/kernel/ptrace.c
+++ b/arch/arm64/kernel/ptrace.c
@@ -1447,8 +1447,8 @@ static const struct user_regset aarch64_regsets[] = {
 	},
 	[REGSET_ZA] = { /* SME ZA */
 		.core_note_type = NT_ARM_ZA,
-		.n = DIV_ROUND_UP(ZA_PT_ZA_SIZE(SVE_VQ_MAX), SVE_VQ_BYTES),
-		.size = SVE_VQ_BYTES,
+		.n = 1,
+		.size = ZA_PT_SIZE(SVE_VQ_MAX),
 		.align = SVE_VQ_BYTES,
 		.regset_get = za_get,
 		.set = za_set,

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