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From: Steve Rutherford <srutherford@google.com>
To: Paolo Bonzini <pbonzini@redhat.com>
Cc: Sean Christopherson <seanjc@google.com>,
	LKML <linux-kernel@vger.kernel.org>,
	KVM list <kvm@vger.kernel.org>, Joerg Roedel <joro@8bytes.org>,
	Brijesh Singh <brijesh.singh@amd.com>,
	Tom Lendacky <thomas.lendacky@amd.com>,
	Ashish Kalra <ashish.kalra@amd.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	Ingo Molnar <mingo@redhat.com>, "H. Peter Anvin" <hpa@zytor.com>,
	Borislav Petkov <bp@suse.de>, X86 ML <x86@kernel.org>
Subject: Re: [PATCH v3 2/2] KVM: X86: Introduce KVM_HC_PAGE_ENC_STATUS hypercall
Date: Tue, 4 May 2021 14:16:20 -0700	[thread overview]
Message-ID: <CABayD+eAJjVjoh9GAnvC9z64pL9GnpHomCqXtw_=EPDr=vz7hA@mail.gmail.com> (raw)
In-Reply-To: <55db8e64-763b-9ecc-9c9a-6d840628e763@redhat.com>

On Tue, May 4, 2021 at 1:56 PM Paolo Bonzini <pbonzini@redhat.com> wrote:
>
> On 04/05/21 22:33, Sean Christopherson wrote:
> > On Tue, May 04, 2021, Paolo Bonzini wrote:
> >> On 04/05/21 19:09, Sean Christopherson wrote:
> >>> On Sat, May 01, 2021, Paolo Bonzini wrote:
> >>>> - make it completely independent from migration, i.e. it's just a facet of
> >>>> MSR_KVM_PAGE_ENC_STATUS saying whether the bitmap is up-to-date.  It would
> >>>> use CPUID bit as the encryption status bitmap and have no code at all in KVM
> >>>> (userspace needs to set up the filter and implement everything).
> >>>
> >>> If the bit is purely a "page encryption status is up-to-date", what about
> >>> overloading KVM_HC_PAGE_ENC_STATUS to handle that status update as well?   That
> >>> would eliminate my biggest complaint about having what is effectively a single
> >>> paravirt feature split into two separate, but intertwined chunks of ABI.
> >>
> >> It's true that they are intertwined, but I dislike not having a way to read
> >> the current state.
> >
> >  From the guest?
>
> Yes, host userspace obviously doesn't need one since it's implemented
> through an MSR filter.  It may not be really necessary to read it, but
> it's a bit jarring compared to how the rest of the PV APIs uses MSRs.
>
> Also from a debugging/crashdump point of view the VMM may have an
> established way to read an MSR from a vCPU, but it won't work if you
> come up with a new way to set the state.

Agreed on the preference for an MSR. I particularly appreciate that it
reduces the kernel footprint for these changes.


Steve

      reply	other threads:[~2021-05-04 21:16 UTC|newest]

Thread overview: 12+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-04-29 10:47 [PATCH v3 0/2] KVM: x86: guest interface for SEV live migration Paolo Bonzini
2021-04-29 10:47 ` [PATCH v3 1/2] KVM: x86: add MSR_KVM_MIGRATION_CONTROL Paolo Bonzini
2021-04-29 10:47 ` [PATCH v3 2/2] KVM: X86: Introduce KVM_HC_PAGE_ENC_STATUS hypercall Paolo Bonzini
2021-04-30 20:10   ` Sean Christopherson
2021-05-01  9:01     ` Paolo Bonzini
2021-05-03 23:22       ` Steve Rutherford
2021-05-04  8:06         ` Paolo Bonzini
2021-05-04 17:09       ` Sean Christopherson
2021-05-04 20:27         ` Paolo Bonzini
2021-05-04 20:33           ` Sean Christopherson
2021-05-04 20:56             ` Paolo Bonzini
2021-05-04 21:16               ` Steve Rutherford [this message]

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