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[2607:7c80:54:e::133]) by mx.google.com with ESMTPS id e17si14635459pgv.422.2019.04.23.11.57.34 for (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Tue, 23 Apr 2019 11:57:34 -0700 (PDT) Received-SPF: pass (google.com: best guess record for domain of peterz@infradead.org designates 2607:7c80:54:e::133 as permitted sender) client-ip=2607:7c80:54:e::133; Authentication-Results: mx.google.com; dkim=pass header.i=@infradead.org header.s=bombadil.20170209 header.b=Ss3LFszE; spf=pass (google.com: best guess record for domain of peterz@infradead.org designates 2607:7c80:54:e::133 as permitted sender) smtp.mailfrom=peterz@infradead.org DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=bombadil.20170209; h=In-Reply-To:Content-Transfer-Encoding :Content-Type:MIME-Version:References:Message-ID:Subject:Cc:To:From:Date: Sender:Reply-To:Content-ID:Content-Description:Resent-Date:Resent-From: Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Id:List-Help: List-Unsubscribe:List-Subscribe:List-Post:List-Owner:List-Archive; bh=WoxsYSmFBK83nDtbePAM0iRr5J/WBY7aawmE+1nqSWU=; b=Ss3LFszEbU35ZOvSDIV3uQWCkx Y6+GBmaYB034wqO+CDQR9qAVPnPIU3prlR0mQR/3NQ1HgukaFzcZE31bR5kTix8yWlTHdHKlksCft aoGlU5s1XeRtzXCCbQgs2iIjfyXCUe4R1KOE6E7iWz+Fz6Gd7kVViO1H8AfpUdNQAiryU3nzTDCom S81V4NEmVoI2vVAoGwr+1L+Mg4aRxGbQOst2Pf4opp+n0Ip36FsLWHP2a1U5CFK7rpTEmSTEXgGWV XbIlZ6M64nYfKc69S7jD9LbAsgwonYf3kBgIpqCcSbxVmVKS1RgZ/i2xgn4rbLnc7y8xoX5zEih2S hsGsQUNw==; Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=hirez.programming.kicks-ass.net) by bombadil.infradead.org with esmtpsa (Exim 4.90_1 #2 (Red Hat Linux)) id 1hJ0bi-0006mE-MZ; Tue, 23 Apr 2019 18:57:30 +0000 Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id 8798929C3F389; Tue, 23 Apr 2019 20:57:28 +0200 (CEST) Date: Tue, 23 Apr 2019 20:57:28 +0200 From: Peter Zijlstra To: Andy Lutomirski Cc: Randy Dunlap , akpm@linux-foundation.org, broonie@kernel.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-next@vger.kernel.org, mhocko@suse.cz, mm-commits@vger.kernel.org, sfr@canb.auug.org.au, Josh Poimboeuf , Linus Torvalds , Andy Lutomirski Subject: Re: mmotm 2019-04-19-14-53 uploaded (objtool) Message-ID: <20190423185728.GX14281@hirez.programming.kicks-ass.net> References: <20190419215358.WMVFXV3bT%akpm@linux-foundation.org> <20190423082448.GY11158@hirez.programming.kicks-ass.net> <20190423173912.GJ12232@hirez.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20190423173912.GJ12232@hirez.programming.kicks-ass.net> User-Agent: Mutt/1.10.1 (2018-07-13) X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Tue, Apr 23, 2019 at 07:39:12PM +0200, Peter Zijlstra wrote: > On Tue, Apr 23, 2019 at 09:07:01AM -0700, Andy Lutomirski wrote: > > > diff --git a/arch/x86/include/asm/uaccess.h b/arch/x86/include/asm/uaccess.h > > > index 22ba683afdc2..c82abd6e4ca3 100644 > > > --- a/arch/x86/include/asm/uaccess.h > > > +++ b/arch/x86/include/asm/uaccess.h > > > @@ -427,10 +427,11 @@ do { \ > > > ({ \ > > > __label__ __pu_label; \ > > > int __pu_err = -EFAULT; \ > > > - __typeof__(*(ptr)) __pu_val; \ > > > - __pu_val = x; \ > > > + __typeof__(*(ptr)) __pu_val = (x); \ > > > + __typeof__(ptr) __pu_ptr = (ptr); \ > > > > Hmm. I wonder if this forces the address calculation to be done > > before STAC, which means that gcc can’t use mov ..., %gs:(fancy > > stuff). It probably depends on how clever the optimizer is. Have you > > looked at the generated code? > > I have not; will do before posting the real patch. x86_64-defconfig using gcc-7.3: $ ./compare.sh defconfig-build defconfig-build1 vmlinux compat_fillonedir 228 227 -1,+0 copy_fpstate_to_sigframe 446 448 +2,+0 total 11374268 11374269 +1,+0 $ ./compare.sh defconfig-build defconfig-build1 vmlinux copy_fpstate_to_sigframe ... 0000 ffffffff81027448: 90 nop \ 0000 ffffffff81027448: 8b 15 92 75 a8 01 mov 0x1a87592(%rip),%edx 0000 ffffffff81027449: 90 nop \ 0000 ffffffff8102744a: R_X86_64_PC32 fpu_user_xstate_size-0x4 0000 ffffffff8102744a: 90 nop \ 0000 ffffffff8102744e: 48 01 da add %rbx,%rdx 0000 ffffffff8102744b: 8b 15 8f 75 a8 01 mov 0x1a8758f(%rip),%edx \ 0000 ffffffff81027451: 90 nop 0000 ffffffff8102744d: R_X86_64_PC32 fpu_user_xstate_size-0x4 \ 0000 ffffffff81027452: 90 nop 0000 ffffffff81027451: c7 04 13 45 58 50 46 movl $0x46505845,(%rbx,%rdx,1) \ 0000 ffffffff81027453: 90 nop 0000 ffffffff81027458: 31 d2 xor %edx,%edx \ 0000 ffffffff81027454: c7 02 45 58 50 46 movl $0x46505845,(%rdx) 0000 ffffffff8102745a: 90 nop \ 0000 ffffffff8102745a: 31 d2 xor %edx,%edx 0000 ffffffff8102745b: 90 nop \ 0000 ffffffff8102745c: 90 nop 0000 ffffffff8102745c: 90 nop \ 0000 ffffffff8102745d: 90 nop 0000 ffffffff8102745d: 90 nop \ 0000 ffffffff8102745e: 90 nop 0000 ffffffff8102745e: 90 nop \ 0000 ffffffff8102745f: 90 nop 0000 ffffffff8102745f: 90 nop \ 0000 ffffffff81027460: 90 nop 0000 ffffffff81027460: 90 nop \ 0000 ffffffff81027461: 90 nop 0000 ffffffff81027461: 90 nop \ 0000 ffffffff81027462: 90 nop 0000 ffffffff81027462: 90 nop \ 0000 ffffffff81027463: 90 nop 0000 ffffffff81027463: 31 c9 xor %ecx,%ecx \ 0000 ffffffff81027464: 90 nop ... So yes, it changes some code, but meh.