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Received: from 77-249-17-252.cable.dynamic.v4.ziggo.nl ([77.249.17.252] helo=noisy.programming.kicks-ass.net) by casper.infradead.org with esmtpsa (Exim 4.98 #2 (Red Hat Linux)) id 1tkN73-00000002xxp-1FSx; Tue, 18 Feb 2025 12:54:09 +0000 Received: by noisy.programming.kicks-ass.net (Postfix, from userid 1000) id 30E9E30066A; Tue, 18 Feb 2025 13:54:08 +0100 (CET) Date: Tue, 18 Feb 2025 13:54:08 +0100 From: Peter Zijlstra To: Shuai Xue Cc: tony.luck@intel.com, bp@alien8.de, nao.horiguchi@gmail.com, tglx@linutronix.de, mingo@redhat.com, dave.hansen@linux.intel.com, x86@kernel.org, hpa@zytor.com, linmiaohe@huawei.com, akpm@linux-foundation.org, jpoimboe@kernel.org, linux-edac@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, baolin.wang@linux.alibaba.com, tianruidong@linux.alibaba.com Subject: Re: [PATCH v2 3/5] x86/mce: add EX_TYPE_EFAULT_REG as in-kernel recovery context to fix copy-from-user operations regression Message-ID: <20250218125408.GD40464@noisy.programming.kicks-ass.net> References: <20250217063335.22257-1-xueshuai@linux.alibaba.com> <20250217063335.22257-4-xueshuai@linux.alibaba.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20250217063335.22257-4-xueshuai@linux.alibaba.com> X-Rspam-User: X-Rspamd-Queue-Id: A0B76180010 X-Rspamd-Server: rspam12 X-Stat-Signature: wphqnoggdjddc9wxhh4a7xoutk8of51c X-HE-Tag: 1739883262-147094 X-HE-Meta: U2FsdGVkX1981A5mssMdmmi0v7z96ohW6mexxPs0ldP1vuTNrxNPNlgEhhDiQKvJeARs20wDOVk42xNCcoG4qi1mkXaDz1Fk0PqNGcVVDckWsG7Ja4P6ZpqbIIdVc8sj/o3hIgf1Ls37T5G+i2Xv6aie5kmaFzG+4LosstzxLpbl4ks0koc1b520+U1fTA8UVm5/sztN1cHzNr82dUnm0rOz8Y/QrnIbGxaJT3pr9uypXuezOa5/iguh0EdImHy18gGb67I+xjcB1pfkWVxHE+mvwMnkm6LvW2aw2MWZd+VhaxOSKgaeaWDBk9BNQqc27gACPoaEp3ywwKIp03/9/lKaPyEp0CH/FmWzRiChzZmB9KxDZxbzVUdkUhsu0gWfiYlOZyIotkpnUuAH91xR37IhhYwJyFY4hVupNJKF0fT8Omay/Mdw2NmhskzHTnBIc5EX2+m7A87xTn17vaPjipkCLvs+U+XUwrMRtvAGG/y2a1mz0zHf3NCDT52pM2bGWQepnCbXMg7URjpsdyq4C7o3aDlm67ztxmkPmRt/QAHqyCxtYB02PHDNQzz5QvVBhrMmMAG6Khx8CwWC362NOdNXr78YRIYnlOAdM9ZhNYpu56MOC/LoUU2JFEwua1jg6DwvptJNhw0OGZF504KouebKb4HpOC60Px8mTWN3CjJdeIzGBxEnQ7XFyc9zBUW4hhNd1rJvng0qTddz8YRINgasNqvQcD9RKzEUz16G/bDY+dt4X3gmpZhTzn9JuWNBfelWoiMOgrfp6ljyBdhzQ2vGQN1asAKgXNKgiCVGOF9WAIjyRUeoDa+KssxwSN9oV7YuPMBMnSAsGjd/67+azLGLamSuPHks+E2CHhb89iY6yvqNZ8rhumQk5gRCXwIvtoK5JDpV6GfxCN1Fvi42HJyXWJcnFVXSG451/Z98WZQ+YXjuXmShupOnSjYYGgX4VgHKXF4w2s/5k4gRPzv JiLL3BK+ oY/NBahHbz1q9exT3n8TD5HgvxZcTGJHlNJ+wd1I/QtYyCyAK3BAToGAjzCb84ucDYtX70Jl1wPIRFPecD9wqa2Zr3qve3mDAgPR0+tgtdxtT4sHR0EL6D3J3Uuh51QvrpOiTnMvfR2D1tG5Ra5rf6EeRUePz29//uZkEwSFleKQyVJO2kr68RMjcbr0YVytwqYggxgnxonwzc4n2zP/R49fh/zIORqZW2xBYQGVJmgD0CEnnyWNK+F9fEtr8WUTePlMmnq2BvQEshZK10GUbpM5UgMme5C8gfLl+DYO2SeAmHW7kSVpNgTqp1g== 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: List-Subscribe: List-Unsubscribe: On Mon, Feb 17, 2025 at 02:33:33PM +0800, Shuai Xue wrote: > diff --git a/arch/x86/kernel/cpu/mce/severity.c b/arch/x86/kernel/cpu/mce/severity.c > index dac4d64dfb2a..14c2d71c3ce1 100644 > --- a/arch/x86/kernel/cpu/mce/severity.c > +++ b/arch/x86/kernel/cpu/mce/severity.c > @@ -16,6 +16,7 @@ > #include > #include > #include > +#include > > #include "internal.h" > > @@ -285,7 +286,8 @@ static bool is_copy_from_user(struct pt_regs *regs) > */ > static noinstr int error_context(struct mce *m, struct pt_regs *regs) > { > - int fixup_type; > + const struct exception_table_entry *e; > + int fixup_type, imm; > bool copy_user; > > if ((m->cs & 3) == 3) > @@ -294,9 +296,14 @@ static noinstr int error_context(struct mce *m, struct pt_regs *regs) > if (!mc_recoverable(m->mcgstatus)) > return IN_KERNEL; > > + e = search_exception_tables(m->ip); > + if (!e) > + return IN_KERNEL; You didn't actually build this, did you? Or did you ignore the extra noinstr warnings? > /* Allow instrumentation around external facilities usage. */ > instrumentation_begin(); > - fixup_type = ex_get_fixup_type(m->ip); > + fixup_type = FIELD_GET(EX_DATA_TYPE_MASK, e->data); > + imm = FIELD_GET(EX_DATA_IMM_MASK, e->data); > copy_user = is_copy_from_user(regs); > instrumentation_end(); > > @@ -304,9 +311,13 @@ static noinstr int error_context(struct mce *m, struct pt_regs *regs) > case EX_TYPE_UACCESS: > if (!copy_user) > return IN_KERNEL; > - m->kflags |= MCE_IN_KERNEL_COPYIN; > - fallthrough; > - > + m->kflags |= MCE_IN_KERNEL_COPYIN | MCE_IN_KERNEL_RECOV; > + return IN_KERNEL_RECOV; > + case EX_TYPE_IMM_REG: > + if (!copy_user || imm != -EFAULT) > + return IN_KERNEL; > + m->kflags |= MCE_IN_KERNEL_COPYIN | MCE_IN_KERNEL_RECOV; > + return IN_KERNEL_RECOV; Maybe I'm justnot understanding things, but what's wrong with something like the below; why do we care about the ex-type if we know its a MOV reading from userspace? The less we muck about with the extable here, the better. --- diff --git a/arch/x86/kernel/cpu/mce/severity.c b/arch/x86/kernel/cpu/mce/severity.c index dac4d64dfb2a..cb021058165f 100644 --- a/arch/x86/kernel/cpu/mce/severity.c +++ b/arch/x86/kernel/cpu/mce/severity.c @@ -300,13 +300,12 @@ static noinstr int error_context(struct mce *m, struct pt_regs *regs) copy_user = is_copy_from_user(regs); instrumentation_end(); - switch (fixup_type) { - case EX_TYPE_UACCESS: - if (!copy_user) - return IN_KERNEL; - m->kflags |= MCE_IN_KERNEL_COPYIN; - fallthrough; + if (copy_user) { + m->kflags |= MCE_IN_KERNEL_COPYIN | MCE_IN_KERNEL_COPYIN; + return IN_KERNEL_RECOV + } + switch (fixup_type) { case EX_TYPE_FAULT_MCE_SAFE: case EX_TYPE_DEFAULT_MCE_SAFE: m->kflags |= MCE_IN_KERNEL_RECOV;