linux-kernel - Re: [PATCH Part2 v6 07/49] x86/sev: Invalid pages from direct map when adding it to RMP table

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Date:   Thu, 5 Jan 2023 15:46:13 -0600
From:   "Kalra, Ashish" <ashish.kalra@....com>
To:     Borislav Petkov <bp@...en8.de>
Cc:     Michael Roth <michael.roth@....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,
        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, jarkko@...nel.org
Subject: Re: [PATCH Part2 v6 07/49] x86/sev: Invalid pages from direct map
 when adding it to RMP table

Hello Boris,

On 12/29/2022 11:09 AM, Borislav Petkov wrote:
> On Tue, Dec 27, 2022 at 03:49:39PM -0600, Kalra, Ashish wrote:
>> Milan onward,
> 
> And before ML there's no SNP, right?
> 

Yes, that's correct.

>> there is H/W support for coherency between mappings of the
>> same physical page with different encryption keys, so AFAIK, there should be
>> no need to flush during page state transitions, where we invoke these direct
>> map interface functions for re-mapping/invalidating pages.
> 
> Yah, that rings a bell.
> 
> In any case, the fact that flushing is not needed should be stated
> somewhere in text so that it is clear why.
> 
>> I don't know if there is any other reason to flush after modifying
>> the direct map ?
> 
> There's
> 
>          /*
>           * No need to flush, when we did not set any of the caching
>           * attributes:
>           */
>          cache = !!pgprot2cachemode(mask_set);
> 
> 
> Does the above HW cover this case too?

Actually, as both set_memory_p() and set_memory_np() are only 
setting/clearing the _PAGE_PRESENT flag and not changing any of the page 
caching attributes so this flush won't be required anyway.

Thanks,
Ashish

> 
> Thx.
>