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[82.69.66.36]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-4772fcf439bsm7028125e9.10.2025.10.30.14.21.52 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 30 Oct 2025 14:21:52 -0700 (PDT) Date: Thu, 30 Oct 2025 21:21:51 +0000 From: David Laight To: Mark Rutland Cc: Markus Elfring , kvmarm@lists.linux.dev, linux-arm-kernel@lists.infradead.org, Catalin Marinas , David Brazdil , Joey Gouly , Marc Zyngier , Oliver Upton , Suzuki Poulouse , Will Deacon , Zenghui Yu , LKML , kernel-janitors@vger.kernel.org, Miaoqian Lin Subject: Re: [PATCH] KVM: arm64: Use pointer from memcpy() call for assignment in init_hyp_mode() Message-ID: <20251030212151.352e9a8a@pumpkin> In-Reply-To: References: <6e962260-5069-490a-89fb-908a4342ccd9@web.de> X-Mailer: Claws Mail 4.1.1 (GTK 3.24.38; arm-unknown-linux-gnueabihf) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit On Thu, 30 Oct 2025 17:49:51 +0000 Mark Rutland wrote: > On Thu, Oct 30, 2025 at 06:11:03PM +0100, Markus Elfring wrote: > > From: Markus Elfring > > Date: Thu, 30 Oct 2025 18:01:41 +0100 > > > > A pointer was assigned to a variable. The same pointer was used for > > the destination parameter of a memcpy() call. > > This function is documented in the way that the same value is returned. > > Thus convert two separate statements into a direct variable assignment for > > the return value from a memory copy action. > > > > The source code was transformed by using the Coccinelle software. > > > > Signed-off-by: Markus Elfring > > --- > > arch/arm64/kvm/arm.c | 4 ++-- > > 1 file changed, 2 insertions(+), 2 deletions(-) > > > > diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c > > index 870953b4a8a7..feab88c31703 100644 > > --- a/arch/arm64/kvm/arm.c > > +++ b/arch/arm64/kvm/arm.c > > @@ -2600,8 +2600,8 @@ static int __init init_hyp_mode(void) > > goto out_err; > > } > > > > - page_addr = page_address(page); > > - memcpy(page_addr, CHOOSE_NVHE_SYM(__per_cpu_start), nvhe_percpu_size()); > > + page_addr = memcpy(page_address(page), CHOOSE_NVHE_SYM(__per_cpu_start), > > + nvhe_percpu_size()); > > This change makes the code harder to read, and harder to modify. It > saves no space. It might save a register spill - but really isn't worth the effort. memcpy() is really best treated as being 'void'. Indeed most implementations would be better if it were 'void'. Although you could define: #define memcpy(d, s, l) ({ auto _d = d; void_memcpy(_d, s, l); _d}) so that the compiler would optimise away the save that memcpy() typically has to do. I even suspect that memcpy() is an old enough function that the return value is 'what the implementation happened to leave in r0'. David > > As Dan said [1]: > > | No one will thank you for making these changes... :( Please don't do > | it. > > [1] https://lore.kernel.org/lkml/aQNsecHJSO2U68Fc@stanley.mountain/ > > Mark. >