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

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Message-ID: <cfd9d16f-6ddf-60d5-f73d-bb49ccd4055f@redhat.com>
Date:   Thu, 22 Oct 2020 15:02:17 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Wanpeng Li <kernellwp@...il.com>, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org
Cc:     Sean Christopherson <sean.j.christopherson@...el.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>
Subject: Re: [PATCH] KVM: X86: Expose KVM_HINTS_REALTIME in
 KVM_GET_SUPPORTED_CPUID

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.

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

Paolo