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From: | Paolo Bonzini |
Subject: | Re: [Qemu-devel] [PATCH 16/23] hyperv: map overlay pages after updating msrs |
Date: | Wed, 14 Jun 2017 14:11:56 +0200 |
User-agent: | Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.1.0 |
On 14/06/2017 13:54, Roman Kagan wrote: >> Why not disable the zeroing for host-initiated MSR writes? This is >> pretty clearly a KVM bug, we can push it to stable kernels too. > > The only problem with this is that QEMU will have no reliable way to > know if the KVM it runs with has this bug fixed or not. Machines > without vmbus work and even migrate fine with the current KVM despite > this bug (the only user of those pages currently is synic timers which > re-arm themselves and post messages regardless of zeroing). Now > updating QEMU to a vmbus-enabled version without updating the kernel > will make the migrations cause guest hangs. Return 2 from KVM_CHECK_EXTENSION(KVM_CAP_HYPERV_SYNIC)? Then you can make new QEMU refuse to enable synic if a new kernel is not available. Paolo
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