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Fri, 31 Jul 2026 16:16:12 -0700 (PDT) Date: Fri, 31 Jul 2026 16:16:11 -0700 In-Reply-To: Mime-Version: 1.0 References: <20260703212145.343527-1-dwmw2@infradead.org> <20260703212145.343527-6-dwmw2@infradead.org> Message-ID: Subject: Re: [PATCH v6 05/36] KVM: x86: Add KVM_[GS]ET_CLOCK_GUEST for accurate KVM clock migration From: Sean Christopherson To: David Woodhouse Cc: Paolo Bonzini , Jonathan Corbet , Shuah Khan , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , x86@kernel.org, "H. Peter Anvin" , Vitaly Kuznetsov , Juergen Gross , Boris Ostrovsky , Paul Durrant , Jonathan Cameron , Sascha Bischoff , Marc Zyngier , Joey Gouly , Jack Allister , Dongli Zhang , joe.jin@oracle.com, kvm@vger.kernel.org, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, xen-devel@lists.xenproject.org, linux-kselftest@vger.kernel.org Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: quoted-printable X-purgate-ID: tlsNG-42698a/1785539774-1A8D99EA-75508FE8/0/0 X-purgate-type: clean X-purgate-size: 755 On Sat, Jul 25, 2026, David Woodhouse wrote: > On Fri, 2026-07-24 at 14:17 -0700, Sean Christopherson wrote: > > On Fri, Jul 03, 2026, David Woodhouse wrote: > > > +4.145 KVM_GET_CLOCK_GUEST > > > +---------------------------- > > > + > > > +:Capability: none > >=20 > > Why not add a CAP?=C2=A0 The check in the subsequent selftest is quite = gross. >=20 > Because nobody would ever use it in practice anyway.=20 Yes, the selftest will. > Even if the ioctl is present, you *still* have to try it and fall back to= the > old method because there are ways that a *guest* can force master clock m= ode > off. That's totally fine, but userspace, especially for selftests, needs a way t= o know the ioctl exists and _should_ work.