Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
Date:   Sat, 28 Aug 2021 22:11:36 +0000
From:   Al Viro <viro@zeniv.linux.org.uk>
To:     Thomas Gleixner <tglx@linutronix.de>
Cc:     "Luck, Tony" <tony.luck@intel.com>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Andreas Gruenbacher <agruenba@redhat.com>,
        Christoph Hellwig <hch@infradead.org>,
        "Darrick J. Wong" <djwong@kernel.org>, Jan Kara <jack@suse.cz>,
        Matthew Wilcox <willy@infradead.org>,
        cluster-devel <cluster-devel@redhat.com>,
        linux-fsdevel <linux-fsdevel@vger.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        ocfs2-devel@oss.oracle.com, Borislav Petkov <bp@alien8.de>,
        x86@kernel.org
Subject: Re: [PATCH v7 05/19] iov_iter: Introduce fault_in_iov_iter_writeable
Message-ID: <YSq0mPAIBfqFC/NE@zeniv-ca.linux.org.uk>
References: <YSkz025ncjhyRmlB@zeniv-ca.linux.org.uk>
 <CAHk-=wh5p6zpgUUoY+O7e74X9BZyODhnsqvv=xqnTaLRNj3d_Q@mail.gmail.com>
 <YSk7xfcHVc7CxtQO@zeniv-ca.linux.org.uk>
 <CAHk-=wjMyZLH+ta5SohAViSc10iPj-hRnHc-KPDoj1XZCmxdBg@mail.gmail.com>
 <YSk+9cTMYi2+BFW7@zeniv-ca.linux.org.uk>
 <YSldx9uhMYhT/G8X@zeniv-ca.linux.org.uk>
 <YSlftta38M4FsWUq@zeniv-ca.linux.org.uk>
 <20210827232246.GA1668365@agluck-desk2.amr.corp.intel.com>
 <87r1edgs2w.ffs@tglx>
 <YSqy+U/3lnF6K0ia@zeniv-ca.linux.org.uk>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <YSqy+U/3lnF6K0ia@zeniv-ca.linux.org.uk>
Sender: Al Viro <viro@ftp.linux.org.uk>
Precedence: bulk

On Sat, Aug 28, 2021 at 10:04:41PM +0000, Al Viro wrote:
> On Sat, Aug 28, 2021 at 11:47:03PM +0200, Thomas Gleixner wrote:
> 
> >   /* Try to handle #PF, but anything else is fatal. */
> >   if (ret != -EFAULT)
> >      return -EINVAL;
> 
> > which all end up in user_insn(). user_insn() returns 0 or the negated
> > trap number, which results in -EFAULT for #PF, but for #MC the negated
> > trap number is -18 i.e. != -EFAULT. IOW, there is no endless loop.
> > 
> > This used to be a problem before commit:
> > 
> >   aee8c67a4faa ("x86/fpu: Return proper error codes from user access functions")
> > 
> > and as the changelog says the initial reason for this was #GP going into
> > the fault path, but I'm pretty sure that I also discussed the #MC angle with
> > Borislav back then. Should have added some more comments there
> > obviously.
> 
> ... or at least have that check spelled
> 
> 	if (ret != -X86_TRAP_PF)
> 		return -EINVAL;
> 
> Unless I'm misreading your explanation, that is...

BTW, is #MC triggered on stored to a poisoned cacheline?  Existence of CLZERO
would seem to argue against that...