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From:   Thomas Gleixner <tglx@linutronix.de>
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To:     Al Viro <viro@zeniv.linux.org.uk>
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
In-Reply-To: <YSqy+U/3lnF6K0ia@zeniv-ca.linux.org.uk>
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 <20210827232246.GA1668365@agluck-desk2.amr.corp.intel.com>
 <87r1edgs2w.ffs@tglx> <YSqy+U/3lnF6K0ia@zeniv-ca.linux.org.uk>
Date:   Sun, 29 Aug 2021 00:23:45 +0200
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On Sat, Aug 28 2021 at 22:04, 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...

Yes, that makes a lot of sense.