From: Sean Christopherson <seanjc@google.com>
To: Michael Roth <michael.roth@amd.com>
Cc: isaku.yamahata@intel.com, kvm@vger.kernel.org,
isaku.yamahata@gmail.com, linux-kernel@vger.kernel.org,
Paolo Bonzini <pbonzini@redhat.com>,
David Matlack <dmatlack@google.com>,
Federico Parola <federico.parola@polito.it>
Subject: Re: [RFC PATCH 0/8] KVM: Prepopulate guest memory API
Date: Mon, 11 Mar 2024 16:44:27 -0700 [thread overview]
Message-ID: <Ze-XW-EbT9vXaagC@google.com> (raw)
In-Reply-To: <20240311032051.prixfnqgbsohns2e@amd.com>
On Sun, Mar 10, 2024, Michael Roth wrote:
> On Fri, Mar 01, 2024 at 09:28:42AM -0800, isaku.yamahata@intel.com wrote:
> > struct kvm_sev_launch_update_data {
> > __u64 uaddr;
> > __u32 len;
> > };
> >
> > - TDX and measurement
> > The TDX correspondence is TDH.MEM.PAGE.ADD and TDH.MR.EXTEND. TDH.MEM.EXTEND
> > extends its measurement by the page contents.
> > Option 1. Add an additional flag like KVM_MEMORY_MAPPING_FLAG_EXTEND to issue
> > TDH.MEM.EXTEND
> > Option 2. Don't handle extend. Let TDX vendor specific API
> > KVM_EMMORY_ENCRYPT_OP to handle it with the subcommand like
> > KVM_TDX_EXTEND_MEMORY.
>
> For SNP this happens unconditionally via SNP_LAUNCH_UPDATE, and with some
> additional measurements via SNP_LAUNCH_FINISH, and down the road when live
> migration support is added that flow will be a bit different. So
> personally I think it's better to leave separate for now.
+1. The only reason to do EXTEND at the same time as PAGE.ADD would be to
optimize setups that want the measurement to be extended with the contents of a
page immediately after the measurement is extended with the mapping metadata for
said page. And AFAIK, the only reason to prefer that approach is for backwards
compatibility, which is not a concern for KVM. I suppose maaaybe some memory
locality performance benefits, but that seems like a stretch.
<time passes>
And I think this whole conversation is moot, because I don't think there's a need
to do PAGE.ADD during KVM_MAP_MEMORY[*]. If KVM_MAP_MEMORY does only the SEPT.ADD
side of things, then both @source (PAGE.ADD) and the EXTEND flag go away.
> But I'd be hesitant to bake more requirements into this pre-mapping
> interface, it feels like we're already overloading it as is.
Agreed. After being able to think more about this ioctl(), I think KVM_MAP_MEMORY
should be as "pure" of a mapping operation as we can make it. It'd be a little
weird that using KVM_MAP_MEMORY is required for TDX VMs, but not other VMs. But
that's really just a reflection of S-EPT, so it's arguably not even a bad thing.
[*] https://lore.kernel.org/all/Ze-TJh0BBOWm9spT@google.com
next prev parent reply other threads:[~2024-03-11 23:44 UTC|newest]
Thread overview: 54+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-03-01 17:28 [RFC PATCH 0/8] KVM: Prepopulate guest memory API isaku.yamahata
2024-03-01 17:28 ` [RFC PATCH 1/8] KVM: Document KVM_MAP_MEMORY ioctl isaku.yamahata
2024-03-07 0:43 ` David Matlack
2024-03-07 1:29 ` Isaku Yamahata
2024-03-07 12:30 ` Huang, Kai
2024-03-07 20:33 ` Isaku Yamahata
2024-03-08 0:20 ` Huang, Kai
2024-03-08 0:56 ` David Matlack
2024-03-08 1:28 ` Sean Christopherson
2024-03-08 2:19 ` Isaku Yamahata
2024-03-10 23:12 ` Michael Roth
2024-03-11 1:05 ` Huang, Kai
2024-03-11 1:08 ` Huang, Kai
2024-03-12 1:34 ` Isaku Yamahata
2024-03-01 17:28 ` [RFC PATCH 2/8] KVM: Add KVM_MAP_MEMORY vcpu ioctl to pre-populate guest memory isaku.yamahata
2024-03-07 0:49 ` David Matlack
2024-03-07 2:52 ` Isaku Yamahata
2024-03-07 12:45 ` Huang, Kai
2024-03-07 20:41 ` Isaku Yamahata
2024-03-11 17:23 ` Sean Christopherson
2024-03-11 22:19 ` Isaku Yamahata
2024-03-01 17:28 ` [RFC PATCH 3/8] KVM: x86/mmu: Introduce initialier macro for struct kvm_page_fault isaku.yamahata
2024-03-11 17:24 ` Sean Christopherson
2024-03-11 22:56 ` Isaku Yamahata
2024-03-01 17:28 ` [RFC PATCH 4/8] KVM: x86/mmu: Factor out kvm_mmu_do_page_fault() isaku.yamahata
2024-03-01 17:28 ` [RFC PATCH 5/8] KVM: x86/mmu: Introduce kvm_mmu_map_page() for prepopulating guest memory isaku.yamahata
2024-03-07 0:38 ` David Matlack
2024-03-19 15:53 ` Isaku Yamahata
2024-03-11 17:29 ` Sean Christopherson
2024-03-11 22:57 ` Isaku Yamahata
2024-03-01 17:28 ` [RFC PATCH 6/8] KVM: x86: Implement kvm_arch_{, pre_}vcpu_map_memory() isaku.yamahata
2024-03-07 0:30 ` David Matlack
2024-03-07 0:36 ` David Matlack
2024-03-07 1:51 ` Isaku Yamahata
2024-03-19 16:26 ` Isaku Yamahata
2024-04-03 23:15 ` Sean Christopherson
2024-03-07 1:34 ` Isaku Yamahata
2024-03-11 23:26 ` Sean Christopherson
2024-03-12 12:38 ` Huang, Kai
2024-03-12 14:20 ` Sean Christopherson
2024-03-12 21:41 ` Huang, Kai
2024-03-12 21:46 ` Huang, Kai
2024-03-12 23:03 ` Sean Christopherson
2024-03-01 17:28 ` [RFC PATCH 7/8] KVM: x86: Add hooks in kvm_arch_vcpu_map_memory() isaku.yamahata
2024-03-01 17:28 ` [RFC PATCH 8/8] KVM: selftests: x86: Add test for KVM_MAP_MEMORY isaku.yamahata
2024-03-07 0:53 ` [RFC PATCH 0/8] KVM: Prepopulate guest memory API David Matlack
2024-03-07 2:09 ` Isaku Yamahata
2024-03-19 16:33 ` Isaku Yamahata
2024-04-03 18:30 ` Sean Christopherson
2024-04-03 22:00 ` Isaku Yamahata
2024-04-03 22:42 ` Sean Christopherson
2024-03-11 3:20 ` Michael Roth
2024-03-11 23:44 ` Sean Christopherson [this message]
2024-03-12 1:32 ` Isaku Yamahata
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