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[35.185.214.157]) by smtp.gmail.com with ESMTPSA id x2sm8512158pgo.2.2021.12.20.09.30.08 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 20 Dec 2021 09:30:08 -0800 (PST) Date: Mon, 20 Dec 2021 17:30:05 +0000 From: Sean Christopherson To: Peter Zijlstra Cc: mingo@redhat.com, tglx@linutronix.de, juri.lelli@redhat.com, vincent.guittot@linaro.org, dietmar.eggemann@arm.com, rostedt@goodmis.org, bsegall@google.com, mgorman@suse.de, bristot@redhat.com, linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-api@vger.kernel.org, x86@kernel.org, pjt@google.com, posk@google.com, avagin@google.com, jannh@google.com, tdelisle@uwaterloo.ca, posk@posk.io Subject: Re: [RFC][PATCH 2/3] x86/uaccess: Implement unsafe_try_cmpxchg_user() Message-ID: References: <20211214204445.665580974@infradead.org> <20211214205358.643980924@infradead.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20211214205358.643980924@infradead.org> X-Rspamd-Server: rspam09 X-Rspamd-Queue-Id: B7310A0042 X-Stat-Signature: sexkmhthsm9w6dmt996jkeotxqorkyfz Authentication-Results: imf15.hostedemail.com; dkim=pass header.d=google.com header.s=20210112 header.b=kwoHClqL; spf=pass (imf15.hostedemail.com: domain of seanjc@google.com designates 209.85.216.52 as permitted sender) smtp.mailfrom=seanjc@google.com; dmarc=pass (policy=reject) header.from=google.com X-HE-Tag: 1640021403-35082 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000199, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Tue, Dec 14, 2021, Peter Zijlstra wrote: > Do try_cmpxchg() loops on userspace addresses. > > Signed-off-by: Peter Zijlstra (Intel) > --- > @@ -501,6 +543,21 @@ do { \ > } while (0) > #endif // CONFIG_CC_HAS_ASM_GOTO_OUTPUT > > +extern void __try_cmpxchg_user_wrong_size(void); > + > +#define unsafe_try_cmpxchg_user(_ptr, _oldp, _nval, _label) ({ \ > + __typeof__(*(_ptr)) __ret; \ > + switch (sizeof(__ret)) { \ > + case 4: __ret = __try_cmpxchg_user_asm("l", (_ptr), (_oldp), \ > + (_nval), _label); \ > + break; \ > + case 8: __ret = __try_cmpxchg_user_asm("q", (_ptr), (_oldp), \ > + (_nval), _label); \ > + break; \ Can we add support for 1-byte and 2-byte cmpxchg, and for using cmpxchg8b to handle 8-byte operations in 32-bit mode? Support for all the flavors (except 16-byte) would allow KVM to use this in an emulator path that currently kmaps the target. I'd be more than happy to help test the result. Thanks! > + default: __try_cmpxchg_user_wrong_size(); \ > + } \ > + __ret; }) > + > /* > * We want the unsafe accessors to always be inlined and use > * the error labels - thus the macro games. > >