From: "Tian, Kevin" <kevin.tian@intel.com>
To: Paolo Bonzini <pbonzini@redhat.com>,
Thomas Gleixner <tglx@linutronix.de>,
"Wang, Wei W" <wei.w.wang@intel.com>,
"quintela@redhat.com" <quintela@redhat.com>
Cc: LKML <linux-kernel@vger.kernel.org>,
"Dr. David Alan Gilbert" <dgilbert@redhat.com>,
Jing Liu <jing2.liu@linux.intel.com>,
"Zhong, Yang" <yang.zhong@intel.com>,
"x86@kernel.org" <x86@kernel.org>,
"kvm@vger.kernel.org" <kvm@vger.kernel.org>, "Christopherson,,
Sean" <seanjc@google.com>,
"Nakajima, Jun" <jun.nakajima@intel.com>,
"Zeng, Guang" <guang.zeng@intel.com>
Subject: RE: [patch 5/6] x86/fpu: Provide fpu_update_guest_xcr0/xfd()
Date: Thu, 16 Dec 2021 01:00:33 +0000 [thread overview]
Message-ID: <BN9PR11MB5276F84FA0C05F00E9A039D38C779@BN9PR11MB5276.namprd11.prod.outlook.com> (raw)
In-Reply-To: <8f37c8a3-1823-0e8f-dc24-6dbae5ce1535@redhat.com>
> From: Paolo Bonzini
> Sent: Wednesday, December 15, 2021 6:41 PM
>
> On 12/15/21 11:27, Paolo Bonzini wrote:
> > On 12/15/21 11:09, Thomas Gleixner wrote:
> >> Lets assume the restore order is XSTATE, XCR0, XFD:
> >>
> >> XSTATE has everything in init state, which means the default
> >> buffer is good enough
> >>
> >> XCR0 has everything enabled including AMX, so the buffer is
> >> expanded
> >>
> >> XFD has AMX disable set, which means the buffer expansion was
> >> pointless
> >>
> >> If we go there, then we can just use a full expanded buffer for KVM
> >> unconditionally and be done with it. That spares a lot of code.
> >
> > If we decide to use a full expanded buffer as soon as KVM_SET_CPUID2 is
> > done, that would work for me.
>
> Off-list, Thomas mentioned doing it even at vCPU creation as long as the
> prctl has been called. That is also okay and even simpler.
Make sense. It also avoids the #GP thing in the emulation path if just due
to reallocation error.
We'll follow this direction to do a quick update/test.
>
> There's also another important thing that hasn't been mentioned so far:
> KVM_GET_SUPPORTED_CPUID should _not_ include the dynamic bits in
> CPUID[0xD] if they have not been requested with prctl. It's okay to
> return the AMX bit, but not the bit in CPUID[0xD].
>
will do.
Thanks
Kevin
next prev parent reply other threads:[~2021-12-16 1:00 UTC|newest]
Thread overview: 47+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-12-14 2:50 [patch 0/6] x86/fpu: Preparatory changes for guest AMX support Thomas Gleixner
2021-12-14 2:50 ` [patch 1/6] x86/fpu: Extend fpu_xstate_prctl() with guest permissions Thomas Gleixner
2021-12-14 5:13 ` Tian, Kevin
2021-12-14 10:37 ` Paolo Bonzini
2021-12-14 2:50 ` [patch 2/6] x86/fpu: Prepare guest FPU for dynamically enabled FPU features Thomas Gleixner
2021-12-14 2:50 ` [patch 3/6] x86/fpu: Make XFD initialization in __fpstate_reset() a function argument Thomas Gleixner
2021-12-14 2:50 ` [patch 4/6] x86/fpu: Add guest support to xfd_enable_feature() Thomas Gleixner
2021-12-14 6:05 ` Tian, Kevin
2021-12-14 10:21 ` Paolo Bonzini
2021-12-14 13:15 ` Thomas Gleixner
2021-12-15 5:46 ` Tian, Kevin
2021-12-15 9:53 ` Thomas Gleixner
2021-12-15 10:02 ` Tian, Kevin
2021-12-14 2:50 ` [patch 5/6] x86/fpu: Provide fpu_update_guest_xcr0/xfd() Thomas Gleixner
2021-12-14 6:25 ` Tian, Kevin
2021-12-14 15:09 ` Wang, Wei W
2021-12-14 15:40 ` Thomas Gleixner
2021-12-14 16:11 ` Wang, Wei W
2021-12-14 18:04 ` Thomas Gleixner
2021-12-14 19:07 ` Juan Quintela
2021-12-14 20:28 ` Thomas Gleixner
2021-12-14 21:35 ` Juan Quintela
2021-12-15 2:17 ` Wang, Wei W
2021-12-15 10:09 ` Thomas Gleixner
2021-12-15 10:27 ` Paolo Bonzini
2021-12-15 10:41 ` Paolo Bonzini
2021-12-16 1:00 ` Tian, Kevin [this message]
2021-12-16 5:36 ` Tian, Kevin
2021-12-16 21:07 ` Paolo Bonzini
2021-12-16 10:21 ` Tian, Kevin
2021-12-16 10:24 ` Paolo Bonzini
2021-12-16 10:26 ` Paolo Bonzini
2021-12-16 13:00 ` Tian, Kevin
2021-12-16 1:04 ` Tian, Kevin
2021-12-16 9:34 ` Thomas Gleixner
2021-12-16 9:59 ` Tian, Kevin
2021-12-16 14:12 ` Thomas Gleixner
2021-12-17 15:33 ` Tian, Kevin
2021-12-15 6:14 ` Tian, Kevin
2021-12-14 2:50 ` [patch 6/6] x86/fpu: Provide kvm_sync_guest_vmexit_xfd_state() Thomas Gleixner
2021-12-15 6:35 ` Liu, Jing2
2021-12-15 9:49 ` Thomas Gleixner
2021-12-14 6:50 ` [patch 0/6] x86/fpu: Preparatory changes for guest AMX support Tian, Kevin
2021-12-14 6:52 ` Liu, Jing2
2021-12-14 7:54 ` Tian, Kevin
2021-12-14 10:42 ` Paolo Bonzini
2021-12-14 13:24 ` Thomas Gleixner
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