linux-kernel - Re: [PATCH Part2 RFC v4 27/40] KVM: X86: Add kvm_x86_ops to get the max page level for the TDP

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Date:   Tue, 20 Jul 2021 15:06:00 -0500
From:   Brijesh Singh <brijesh.singh@....com>
To:     Sean Christopherson <seanjc@...gle.com>
Cc:     brijesh.singh@....com, x86@...nel.org,
        linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        linux-efi@...r.kernel.org, platform-driver-x86@...r.kernel.org,
        linux-coco@...ts.linux.dev, linux-mm@...ck.org,
        linux-crypto@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Joerg Roedel <jroedel@...e.de>,
        Tom Lendacky <thomas.lendacky@....com>,
        "H. Peter Anvin" <hpa@...or.com>, Ard Biesheuvel <ardb@...nel.org>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Andy Lutomirski <luto@...nel.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Sergio Lopez <slp@...hat.com>, Peter Gonda <pgonda@...gle.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>,
        David Rientjes <rientjes@...gle.com>,
        Dov Murik <dovmurik@...ux.ibm.com>,
        Tobin Feldman-Fitzthum <tobin@....com>,
        Borislav Petkov <bp@...en8.de>,
        Michael Roth <michael.roth@....com>,
        Vlastimil Babka <vbabka@...e.cz>, tony.luck@...el.com,
        npmccallum@...hat.com, brijesh.ksingh@...il.com
Subject: Re: [PATCH Part2 RFC v4 27/40] KVM: X86: Add kvm_x86_ops to get the
 max page level for the TDP



On 7/20/21 2:38 PM, Sean Christopherson wrote:
...

> 
> The other option is to use vm_type, which TDX is already planning on leveraging.
> Paolo raised the question of whether or not the TDX type could be reused for SNP.
> We should definitely sort that out before merging either series.  I'm personally
> in favor of separating TDX and SNP, it seems inevitable that common code will
> want to differentiate between the two.

Yes, I did saw that and it seems much better.

> 
> https://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Flkml.kernel.org%2Fr%2F8eb87cd52a89d957af03f93a9ece5634426a7757.1625186503.git.isaku.yamahata%40intel.com&amp;data=04%7C01%7Cbrijesh.singh%40amd.com%7Cb658fcf339234fd9030d08d94bb5edf1%7C3dd8961fe4884e608e11a82d994e183d%7C0%7C0%7C637624067039647374%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&amp;sdata=tdVALNsQGer0Z69%2FyYaRqWYZvH27k%2BmgHdslQlJ7qlU%3D&amp;reserved=0
> 

...

>>
>> There is yet another reason why we can't avoid the PSMASH after doing
>> everything to ensure that NPT and RMP are in sync. e.g if NPT and RMP
>> are programmed with 2mb size but the guest tries to PVALIDATE the page
>> as a 4k. In that case, we will see #NPF with page size mismatch and have
>> to perform psmash.
> 
> Boo, there's no way to communicate to the guest that it's doing PVALIDATE wrong
> is there?
> 

if the guest chooses smaller page-size then we don't have any means to 
notify the guest; the hardware will cause an #NPF and its up to the 
hypervisor to resolve the fault.

However, if the guest attempts to validate with the larger page-level 
(e.g guest using 2mb and RMP entry was 4k) then PVALIDATE will return 
SIZEMISMATCH error to the guest.

thanks