linux-kernel - Re: [PATCH] kvm/x86: reserve bit KVM_HINTS_PHYS_ADDRESS_SIZE_DATA

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Message-ID: <2db45546-d504-d006-ce3c-65f832b5a70a@redhat.com>
Date:   Thu, 22 Sep 2022 14:24:04 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Jim Mattson <jmattson@...gle.com>,
        Sean Christopherson <seanjc@...gle.com>
Cc:     Gerd Hoffmann <kraxel@...hat.com>, kvm@...r.kernel.org,
        Wanpeng Li <wanpengli@...cent.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        "maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)" <x86@...nel.org>,
        "H. Peter Anvin" <hpa@...or.com>,
        "open list:X86 ARCHITECTURE (32-BIT AND 64-BIT)" 
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] kvm/x86: reserve bit
 KVM_HINTS_PHYS_ADDRESS_SIZE_DATA_VALID

On 9/21/22 18:32, Jim Mattson wrote:
>> The issue is that this "hint" effectively breaks other VMMs that already provide
>> an accurate guest.MAXPHYADDR.
>
> Any VMM that doesn't provide an accurate guest.MAXPHYADDR is broken.
> Why do we need a "hint" that the virtual processor works?

I agree.  Since old (and current) versions of QEMU wouldn't get the bit 
anyway, just fix the next one.  I'll follow up on the QEMU mailing list.

Paolo