linux-kernel - Re: [PATCH 0/3] KVM: x86: KVM_MEM_PCI

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Message-ID: <87wo2cngv6.fsf@vitty.brq.redhat.com>
Date:   Thu, 06 Aug 2020 13:39:09 +0200
From:   Vitaly Kuznetsov <vkuznets@...hat.com>
To:     "Michael S. Tsirkin" <mst@...hat.com>
Cc:     kvm@...r.kernel.org, Paolo Bonzini <pbonzini@...hat.com>,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Peter Xu <peterx@...hat.com>,
        Julia Suvorova <jsuvorov@...hat.com>,
        Andy Lutomirski <luto@...nel.org>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/3] KVM: x86: KVM_MEM_PCI_HOLE memory

"Michael S. Tsirkin" <mst@...hat.com> writes:

> About the feature bit, I am not sure why it's really needed. A single
> mmio access is cheaper than two io accesses anyway, right? So it makes
> sense for a kvm guest whether host has this feature or not.
> We need to be careful and limit to a specific QEMU implementation
> to avoid tripping up bugs, but it seems more appropriate to
> check it using pci host IDs.

Right, it's just that "running on KVM" is too coarse grained, we just
need a way to somehow distinguish between "known/good" and
"unknown/buggy" configurations.

-- 
Vitaly