From: Paolo Bonzini <pbonzini@redhat.com>
To: Sean Christopherson <seanjc@google.com>
Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
Thomas Gleixner <tglx@linutronix.de>,
Dave Hansen <dave.hansen@intel.com>,
Borislav Petkov <bp@alien8.de>, Andy Lutomirski <luto@kernel.org>,
Kuppuswamy Sathyanarayanan
<sathyanarayanan.kuppuswamy@linux.intel.com>,
Elena Reshetova <elena.reshetova@intel.com>,
Jun Nakajima <jun.nakajima@intel.com>,
x86@kernel.org, linux-coco@lists.linux.dev,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH] x86/tdx: Mark TSC reliable
Date: Thu, 7 Sep 2023 19:25:01 +0200 [thread overview]
Message-ID: <CABgObfZE+1AkEPyXzQQCV5Ssho5hMrBvAi5rFdTKNNAAijhRjw@mail.gmail.com> (raw)
In-Reply-To: <ZOjF2DMBgW/zVvL3@google.com>
On Fri, Aug 25, 2023 at 5:25 PM Sean Christopherson <seanjc@google.com> wrote:
> > > TDX aside it might be useful to have a mechanism to select TSC over KVM
> > > clock in general.
> >
> > Sean, Paolo, any comment on this?
>
> I would expect the VMM to not advertise KVM clock if the VM is going to run on
> hosts with stable TSCs, i.e. the guest really shouldn't need to do anything in.
> But I avoid clocks and timekeeping like the plague, so take that with a grain of
> salt, e.g. maybe there's a good reason to always advertise kvmclock.
Mostly because users avoid clocks and timekeeping _even more_;
advertising kvmclock is safe in general, so userspace does it in case
the VM is later migrated to a machine with unstable TSC.
> For TDX and other paranoid guests, I assume the kernel command line is captured
> as part of attestation. And so the existing "no-kvmclock" param should be
> sufficient to ensure the guest doesn't use KVM clock over the TSC, though IIRC
> TDX requires a constant, non-stop TSC, so it's likely not strictly necessary.
As Kirill said, the guest still has to protect itself, so the patch
makes sense (I see a v2 has been posted in the meanwhile).
Paolo
prev parent reply other threads:[~2023-09-07 17:25 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-08-08 16:23 [PATCH] x86/tdx: Mark TSC reliable Kirill A. Shutemov
2023-08-08 17:13 ` Dave Hansen
2023-08-08 20:01 ` Kirill A. Shutemov
2023-08-09 5:44 ` Reshetova, Elena
2023-08-09 6:13 ` Kirill A. Shutemov
2023-08-22 23:39 ` Erdem Aktas
2023-08-24 15:49 ` Thomas Gleixner
2023-08-25 13:52 ` Kirill A. Shutemov
2023-08-25 17:09 ` Thomas Gleixner
2023-08-29 16:01 ` Nakajima, Jun
2023-08-30 7:33 ` Thomas Gleixner
2023-08-31 15:16 ` Nakajima, Jun
2023-08-24 19:31 ` Thomas Gleixner
2023-08-25 13:47 ` Kirill A. Shutemov
2023-08-25 15:16 ` Sean Christopherson
2023-09-07 17:25 ` Paolo Bonzini [this message]
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