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Fri, 07 Mar 2025 08:19:54 -0800 (PST) Date: Fri, 7 Mar 2025 19:19:52 +0300 From: Alexey Dobriyan To: Dave Hansen Cc: tglx@linutronix.de, mingo@redhat.com, bp@alien8.de, dave.hansen@linux.intel.com, x86@kernel.org, hpa@zytor.com, linux-kernel@vger.kernel.org Subject: Re: [PATCH 1/4] x86/asm: inline constant inputs in rdpkru(), wrpkru() Message-ID: <360f4fcc-8141-449c-a5fc-cd91182e0899@p183> References: <20250306210710.3403-1-adobriyan@gmail.com> <3e354397-1666-4d63-b863-ef9f9d31fa37@intel.com> 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=utf-8 Content-Disposition: inline In-Reply-To: <3e354397-1666-4d63-b863-ef9f9d31fa37@intel.com> On Thu, Mar 06, 2025 at 01:35:01PM -0800, Dave Hansen wrote: > On 3/6/25 13:07, Alexey Dobriyan wrote: > > static inline void wrpkru(u32 pkru) > > { > > - u32 ecx = 0, edx = 0; > > - > > /* > > * "wrpkru" instruction. Loads contents in EAX to PKRU, > > * requires that ecx = edx = 0. > > */ > > asm volatile(".byte 0x0f,0x01,0xef\n\t" > > - : : "a" (pkru), "c"(ecx), "d"(edx)); > > + : : "a" (pkru), "c" (0), "d" (0)); > > } > > Hey Alexey, > > I appreciate the patch. But I do like how it's written currently. I > honestly kinda wish it went even further and did: > > u32 eax = pkru; I _think_ you can write "eax" (pkru) . I don't like the comment either. It just reiterates the SDM. Trailing \n\t too -- they don't do anything in one-liners. The function is basically: // wrpkru asm volatile ( ".byte 0x0f,0x01,0xef" : : "a" (pkru), "d" (0) , "c" (0) );