linux-kernel - Re: [PATCH v13 5/5] arm64: introduce copy_mc_to

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Message-ID: <Z6zX3Ro60sMH7C13@arm.com>
Date: Wed, 12 Feb 2025 17:18:21 +0000
From: Catalin Marinas <catalin.marinas@....com>
To: Tong Tiangen <tongtiangen@...wei.com>
Cc: Mark Rutland <mark.rutland@....com>,
	Jonathan Cameron <Jonathan.Cameron@...wei.com>,
	Mauro Carvalho Chehab <mchehab+huawei@...nel.org>,
	Will Deacon <will@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	James Morse <james.morse@....com>,
	Robin Murphy <robin.murphy@....com>,
	Andrey Konovalov <andreyknvl@...il.com>,
	Dmitry Vyukov <dvyukov@...gle.com>,
	Vincenzo Frascino <vincenzo.frascino@....com>,
	Michael Ellerman <mpe@...erman.id.au>,
	Nicholas Piggin <npiggin@...il.com>,
	Andrey Ryabinin <ryabinin.a.a@...il.com>,
	Alexander Potapenko <glider@...gle.com>,
	Christophe Leroy <christophe.leroy@...roup.eu>,
	"Aneesh Kumar K.V" <aneesh.kumar@...nel.org>,
	"Naveen N. Rao" <naveen.n.rao@...ux.ibm.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
	Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
	"H. Peter Anvin" <hpa@...or.com>,
	Madhavan Srinivasan <maddy@...ux.ibm.com>,
	linux-arm-kernel@...ts.infradead.org, linux-mm@...ck.org,
	linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org,
	kasan-dev@...glegroups.com, wangkefeng.wang@...wei.com,
	Guohanjun <guohanjun@...wei.com>
Subject: Re: [PATCH v13 5/5] arm64: introduce copy_mc_to_kernel()
 implementation

On Mon, Dec 09, 2024 at 10:42:57AM +0800, Tong Tiangen wrote:
> The copy_mc_to_kernel() helper is memory copy implementation that handles
> source exceptions. It can be used in memory copy scenarios that tolerate
> hardware memory errors(e.g: pmem_read/dax_copy_to_iter).
> 
> Currently, only x86 and ppc support this helper, Add this for ARM64 as
> well, if ARCH_HAS_COPY_MC is defined, by implementing copy_mc_to_kernel()
> and memcpy_mc() functions.
> 
> Because there is no caller-saved GPR is available for saving "bytes not
> copied" in memcpy(), the memcpy_mc() is referenced to the implementation
> of copy_from_user(). In addition, the fixup of MOPS insn is not considered
> at present.

Same question as on the previous patch, can we not avoid the memcpy()
duplication if the only difference is entries in the exception table?
IIUC in patch 2 fixup_exception() even ignores the new type. The error
must come on the do_sea() path.

-- 
Catalin