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

From: Brijesh Singh <brijesh.singh@amd.com>
To: Sean Christopherson <seanjc@google.com>
Cc: brijesh.singh@amd.com, x86@kernel.org,
	linux-kernel@vger.kernel.org, kvm@vger.kernel.org,
	linux-efi@vger.kernel.org, platform-driver-x86@vger.kernel.org,
	linux-coco@lists.linux.dev, linux-mm@kvack.org,
	linux-crypto@vger.kernel.org,
	Thomas Gleixner <tglx@linutronix.de>,
	Ingo Molnar <mingo@redhat.com>, Joerg Roedel <jroedel@suse.de>,
	Tom Lendacky <thomas.lendacky@amd.com>,
	"H. Peter Anvin" <hpa@zytor.com>,
	Ard Biesheuvel <ardb@kernel.org>,
	Paolo Bonzini <pbonzini@redhat.com>,
	Vitaly Kuznetsov <vkuznets@redhat.com>,
	Wanpeng Li <wanpengli@tencent.com>,
	Jim Mattson <jmattson@google.com>,
	Andy Lutomirski <luto@kernel.org>,
	Dave Hansen <dave.hansen@linux.intel.com>,
	Sergio Lopez <slp@redhat.com>, Peter Gonda <pgonda@google.com>,
	Peter Zijlstra <peterz@infradead.org>,
	Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>,
	David Rientjes <rientjes@google.com>,
	Dov Murik <dovmurik@linux.ibm.com>,
	Tobin Feldman-Fitzthum <tobin@ibm.com>,
	Borislav Petkov <bp@alien8.de>,
	Michael Roth <michael.roth@amd.com>,
	Vlastimil Babka <vbabka@suse.cz>,
	tony.luck@intel.com, npmccallum@redhat.com,
	brijesh.ksingh@gmail.com
Subject: Re: [PATCH Part2 RFC v4 27/40] KVM: X86: Add kvm_x86_ops to get the max page level for the TDP
Date: Tue, 20 Jul 2021 15:06:00 -0500	[thread overview]
Message-ID: <afa7bd42-ce18-c89e-3f54-cbf197143678@amd.com> (raw)
In-Reply-To: <YPcmJuKHFYjCgpqd@google.com>

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