linux-kernel - Re: Thoughts of AMX KVM support based on latest kernel

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Date:   Wed, 17 Nov 2021 00:35:51 +0100
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Sean Christopherson <seanjc@...gle.com>
Cc:     "Liu, Jing2" <jing2.liu@...el.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        LKML <linux-kernel@...r.kernel.org>,
        "x86@...nel.org" <x86@...nel.org>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "Nakajima, Jun" <jun.nakajima@...el.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Arjan van de Ven <arjan@...ux.intel.com>,
        Jing Liu <jing2.liu@...ux.intel.com>,
        "Cooper, Andrew" <andrew.cooper3@...rix.com>,
        "Bae, Chang Seok" <chang.seok.bae@...el.com>
Subject: Re: Thoughts of AMX KVM support based on latest kernel

On Tue, Nov 16 2021 at 20:12, Sean Christopherson wrote:
> On Tue, Nov 16, 2021, Thomas Gleixner wrote:
>> Now you could argue that the interrupt/softirq XSAVES should also read
>> the XFD MSR and save it in guest_fpstate.xfd. Same in schedule()
>> and kvm_put_guest_fpu(), i.e:
>> 
>>       XSAVES
>>       if (fpstate->is_guest) {
>>             rdmsrl(XFD, xfd);
>>             fpstate->xfd = xfd;
>>             __this_cpu_write(..., xfd);
>>       }
>> 
>> We can do that, but I'm unhappy about this conditional in schedule(). So
>> I was asking for doing a simple KVM only solution first:
>
> Ah, the schedule() conditional is the part I was missing.  Thanks!

As I was missing the preempt notifier... which makes it a different
story, but I still think that the simple version is good enough at least
for a start.

Thanks,

        tglx