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Date:   Thu, 23 Sep 2021 10:14:42 -0700
From:   "Luck, Tony" <tony.luck@intel.com>
To:     Peter Zijlstra <peterz@infradead.org>
Cc:     Fenghua Yu <fenghua.yu@intel.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
        Andy Lutomirski <luto@kernel.org>,
        Dave Hansen <dave.hansen@intel.com>,
        Lu Baolu <baolu.lu@linux.intel.com>,
        Joerg Roedel <joro@8bytes.org>,
        Josh Poimboeuf <jpoimboe@redhat.com>,
        Dave Jiang <dave.jiang@intel.com>,
        Jacob Jun Pan <jacob.jun.pan@intel.com>,
        Ashok Raj <ashok.raj@intel.com>,
        Ravi V Shankar <ravi.v.shankar@intel.com>,
        iommu@lists.linux-foundation.org, x86 <x86@kernel.org>,
        linux-kernel <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 4/8] x86/traps: Demand-populate PASID MSR via #GP
Message-ID: <YUy2AmabA4ODOgAC@agluck-desk2.amr.corp.intel.com>
References: <20210920192349.2602141-1-fenghua.yu@intel.com>
 <20210920192349.2602141-5-fenghua.yu@intel.com>
 <20210922210722.GV4323@worktop.programming.kicks-ass.net>
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On Wed, Sep 22, 2021 at 11:07:22PM +0200, Peter Zijlstra wrote:
> On Mon, Sep 20, 2021 at 07:23:45PM +0000, Fenghua Yu wrote:
> > @@ -538,6 +547,9 @@ DEFINE_IDTENTRY_ERRORCODE(exc_general_protection)
> >  
> >  	cond_local_irq_enable(regs);
> >  
> > +	if (user_mode(regs) && fixup_pasid_exception())
> > +		goto exit;
> > +

> So you're eating any random #GP that might or might not be PASID
> related. And all that witout a comment... Enlighten?

This is moderately well commented inside the fixup_pasid_exception()
function. Another copy of the comments here at the call-site seems
overkill.

Would it help to change the name to try_fixup_pasid_exception()
to make it clearer that this is just a heuristic that may or may
not fix this particular #GP?

-Tony