From:   Thomas Gleixner <tglx@linutronix.de>
To:     Sean Christopherson <seanjc@google.com>
Cc:     "Liu, Jing2" <jing2.liu@intel.com>,
        Paolo Bonzini <pbonzini@redhat.com>,
        LKML <linux-kernel@vger.kernel.org>,
        "x86@kernel.org" <x86@kernel.org>,
        "kvm@vger.kernel.org" <kvm@vger.kernel.org>,
        "Nakajima, Jun" <jun.nakajima@intel.com>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        Arjan van de Ven <arjan@linux.intel.com>,
        Jing Liu <jing2.liu@linux.intel.com>,
        "Cooper, Andrew" <andrew.cooper3@citrix.com>,
        "Bae, Chang Seok" <chang.seok.bae@intel.com>
Subject: Re: Thoughts of AMX KVM support based on latest kernel
In-Reply-To: <YZQQuQDWPhcJG6pM@google.com>
References: <BYAPR11MB325685AB8E3DFD245846F854A9939@BYAPR11MB3256.namprd11.prod.outlook.com>
 <87k0h85m65.ffs@tglx> <YZPWsICdDTZ02UDu@google.com> <87ee7g53rp.ffs@tglx>
 <YZQQuQDWPhcJG6pM@google.com>
Date:   Wed, 17 Nov 2021 00:35:51 +0100
Message-ID: <87wnl74qso.ffs@tglx>
MIME-Version: 1.0
Content-Type: text/plain
Precedence: bulk

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