linux-kernel - Re: [PATCH Part2 v6 09/49] x86/fault: Add support to handle the RMP fault for user address

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Date:   Tue, 6 Sep 2022 13:25:06 +0300
From:   Jarkko Sakkinen <jarkko@...nel.org>
To:     Borislav Petkov <bp@...en8.de>
Cc:     Ashish Kalra <Ashish.Kalra@....com>, x86@...nel.org,
        linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        linux-coco@...ts.linux.dev, linux-mm@...ck.org,
        linux-crypto@...r.kernel.org, tglx@...utronix.de, mingo@...hat.com,
        jroedel@...e.de, thomas.lendacky@....com, hpa@...or.com,
        ardb@...nel.org, pbonzini@...hat.com, seanjc@...gle.com,
        vkuznets@...hat.com, jmattson@...gle.com, luto@...nel.org,
        dave.hansen@...ux.intel.com, slp@...hat.com, pgonda@...gle.com,
        peterz@...radead.org, srinivas.pandruvada@...ux.intel.com,
        rientjes@...gle.com, dovmurik@...ux.ibm.com, tobin@....com,
        michael.roth@....com, vbabka@...e.cz, kirill@...temov.name,
        ak@...ux.intel.com, tony.luck@...el.com, marcorr@...gle.com,
        sathyanarayanan.kuppuswamy@...ux.intel.com, alpergun@...gle.com,
        dgilbert@...hat.com
Subject: Re: [PATCH Part2 v6 09/49] x86/fault: Add support to handle the RMP
 fault for user address

On Tue, Aug 09, 2022 at 06:55:43PM +0200, Borislav Petkov wrote:
> On Mon, Jun 20, 2022 at 11:03:43PM +0000, Ashish Kalra wrote:
> > +	pfn = pte_pfn(*pte);
> > +
> > +	/* If its large page then calculte the fault pfn */
> > +	if (level > PG_LEVEL_4K) {
> > +		unsigned long mask;
> > +
> > +		mask = pages_per_hpage(level) - pages_per_hpage(level - 1);
> > +		pfn |= (address >> PAGE_SHIFT) & mask;
> 
> Oh boy, this is unnecessarily complicated. Isn't this
> 
> 	pfn |= pud_index(address);
> 
> or
> 	pfn |= pmd_index(address);

I played with this a bit and ended up with

        pfn = pte_pfn(*pte) | PFN_DOWN(address & page_level_mask(level - 1));

Unless I got something terribly wrong, this should do the
same (see the attached patch) as the existing calculations.

BR, Jarkko

View attachment "0001-x86-fault-Simplify-PFN-calculation-in-handle_user_rm.patch" of type "text/plain" (1751 bytes)