linux-kernel - Re: [PATCH v7 9/9] x86/mmu: Allocate/free PASID

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Date:   Mon, 14 Sep 2020 18:37:15 +0000
From:   Fenghua Yu <fenghua.yu@...el.com>
To:     Borislav Petkov <bp@...en8.de>
Cc:     Fenghua Yu <fenghua.yu@...el.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, H Peter Anvin <hpa@...or.com>,
        Andy Lutomirski <luto@...nel.org>,
        Jean-Philippe Brucker <jean-philippe@...aro.org>,
        Christoph Hellwig <hch@...radead.org>,
        Peter Zijlstra <peterz@...radead.org>,
        David Woodhouse <dwmw2@...radead.org>,
        Lu Baolu <baolu.lu@...ux.intel.com>,
        Dave Hansen <dave.hansen@...el.com>,
        Tony Luck <tony.luck@...el.com>,
        Ashok Raj <ashok.raj@...el.com>,
        Jacob Jun Pan <jacob.jun.pan@...el.com>,
        Dave Jiang <dave.jiang@...el.com>,
        Sohil Mehta <sohil.mehta@...el.com>,
        Ravi V Shankar <ravi.v.shankar@...el.com>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        x86 <x86@...nel.org>, iommu@...ts.linux-foundation.org
Subject: Re: [PATCH v7 9/9] x86/mmu: Allocate/free PASID

Hi, Boris,

On Mon, Sep 07, 2020 at 01:18:43PM +0200, Borislav Petkov wrote:
> On Thu, Aug 27, 2020 at 08:06:34AM -0700, Fenghua Yu wrote:
> > +		 */
> > +		xsave = &fpu->state.xsave;
> > +		xsave->header.xfeatures |= XFEATURE_MASK_PASID;
> > +		ppasid_state = get_xsave_addr(xsave, XFEATURE_PASID);
> > +		if (ppasid_state) {
> > +			/*
> > +			 * Only update the task's PASID state when it's
> > +			 * different from the mm's pasid.
> > +			 */
> > +			if (ppasid_state->pasid != pasid_state) {
> > +				/*
> > +				 * Invalid fpregs so that xrstors will pick up
> 							  ^^^^^^^
> 
> Not "xrstors" but the "state restoring" or so.

Fixed.

> > +				 * the PASID state.
> > +				 */
> > +				__fpu_invalidate_fpregs_state(fpu);
> > +				ppasid_state->pasid = pasid_state;
> > +			}
> 
> What happens if get_xsave_addr() returns NULL? A WARN_ONCE maybe?

get_xsave_addr() will not return NULL because xsave->header.xfeatures has
XFEATURE_MASK_PASID set. I will remove the unnecessary check "if (ppasid_state)"
to optimize the function and add a comment on why the check is unnecessary.

> Ok, done with review.

I addressed all of your comments and will send out the updated series soon.

Thank you very much for your review!

-Fenghua