linux-kernel - Re: [PATCH] KVM: X86: Expose KVM_HINTS_REALTIME in KVM_GET_SUPPORTED

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Date:   Thu, 22 Oct 2020 09:35:03 -0700
From:   Jim Mattson <jmattson@...gle.com>
To:     Paolo Bonzini <pbonzini@...hat.com>
Cc:     Wanpeng Li <kernellwp@...il.com>,
        LKML <linux-kernel@...r.kernel.org>,
        kvm list <kvm@...r.kernel.org>,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Joerg Roedel <joro@...tes.org>
Subject: Re: [PATCH] KVM: X86: Expose KVM_HINTS_REALTIME in KVM_GET_SUPPORTED_CPUID

On Thu, Oct 22, 2020 at 6:02 AM Paolo Bonzini <pbonzini@...hat.com> wrote:
>
> On 22/10/20 03:34, Wanpeng Li wrote:
> > From: Wanpeng Li <wanpengli@...cent.com>
> >
> > Per KVM_GET_SUPPORTED_CPUID ioctl documentation:
> >
> > This ioctl returns x86 cpuid features which are supported by both the
> > hardware and kvm in its default configuration.
> >
> > A well-behaved userspace should not set the bit if it is not supported.
> >
> > Suggested-by: Jim Mattson <jmattson@...gle.com>
> > Signed-off-by: Wanpeng Li <wanpengli@...cent.com>
>
> It's common for userspace to copy all supported CPUID bits to
> KVM_SET_CPUID2, I don't think this is the right behavior for
> KVM_HINTS_REALTIME.

That is not how the API is defined, but I'm sure you know that. :-)

> (But maybe this was discussed already; if so, please point me to the
> previous discussion).
>
> Paolo