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Re: [PATCH 03/16] x86/tsc: Add helper to register CPU and TSC freq calibration routines
- To: Borislav Petkov <bp@xxxxxxxxx>, Sean Christopherson <seanjc@xxxxxxxxxx>
- From: Tom Lendacky <thomas.lendacky@xxxxxxx>
- Date: Wed, 12 Feb 2025 10:49:52 -0600
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- Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>, Ingo Molnar <mingo@xxxxxxxxxx>, Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>, x86@xxxxxxxxxx, "Kirill A. Shutemov" <kirill.shutemov@xxxxxxxxxxxxxxx>, Juergen Gross <jgross@xxxxxxxx>, "K. Y. Srinivasan" <kys@xxxxxxxxxxxxx>, Haiyang Zhang <haiyangz@xxxxxxxxxxxxx>, Wei Liu <wei.liu@xxxxxxxxxx>, Dexuan Cui <decui@xxxxxxxxxxxxx>, Ajay Kaher <ajay.kaher@xxxxxxxxxxxx>, Jan Kiszka <jan.kiszka@xxxxxxxxxxx>, Paolo Bonzini <pbonzini@xxxxxxxxxx>, Andy Lutomirski <luto@xxxxxxxxxx>, Peter Zijlstra <peterz@xxxxxxxxxxxxx>, linux-kernel@xxxxxxxxxxxxxxx, linux-coco@xxxxxxxxxxxxxxx, virtualization@xxxxxxxxxxxxxxx, linux-hyperv@xxxxxxxxxxxxxxx, kvm@xxxxxxxxxxxxxxx, xen-devel@xxxxxxxxxxxxxxxxxxxx, Nikunj A Dadhania <nikunj@xxxxxxx>
- Delivery-date: Wed, 12 Feb 2025 16:50:06 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 2/11/25 14:32, Borislav Petkov wrote:
> On Tue, Feb 11, 2025 at 09:43:23AM -0800, Sean Christopherson wrote:
>> It conflates two very different things: host/bare metal support for memory
>> encryption, and SEV guest support. For kernels that will never run in a VM,
>> pulling in all the SEV guest code just to enable host-side support for SME
>> (and
>> SEV) is very undesirable.
>
> Well, that might've grown in the meantime... when we started it, it was all
> small so it didn't really matter and we kept it simple. That's why I never
> thought about it. And actually, we've been thinking of even ripping out SME
> in favor of TSME which is transparent and doesn't need any SME glue. But there
> was some reason why we didn't want to do it yet, Tom would know.
I think it was because TSME is a BIOS setting and you don't trust BIOS
to always expose the setting :)
I do have a patch series to remove SME. I haven't updated it in a couple
of releases, so would just need to dust it off and rebase it.
Thanks,
Tom
>
> As to carving it out now, meh, dunno how much savings that would be. Got
> a student to put on that task? :-P
>
>> And in this case, because AMD_MEM_ENCRYPT gates both host and guest code, it
>> can't depend on HYPERVISOR_GUEST like it should, because taking a dependency
>> on
>> HYPERVISOR_GUEST to enable SME is obviously wrong.
>
> Right.
>
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