Re: [Qemu-devel] [PATCH] kvm: Delete the slot only when KVM_MEM_READONLY flag is changed

[Paolo Bonzini]

On 13/06/2018 04:15, Shannon Zhao wrote:
> 
> 
> On 2018/6/12 20:17, Paolo Bonzini wrote:
>> On 16/05/2018 11:18, Shannon Zhao wrote:
>>> According to KVM commit 75d61fbc, it needs to delete the slot before
>>> changing the KVM_MEM_READONLY flag. But QEMU commit 235e8982 only check
>>> whether KVM_MEM_READONLY flag is set instead of changing. It doesn't
>>> need to delete the slot if the KVM_MEM_READONLY flag is not changed.
>>>
>>> This fixes a issue that migrating a VM at the OVMF startup stage and
>>> VM is executing the codes in rom. Between the deleting and adding the
>>> slot in kvm_set_user_memory_region, there is a chance that guest access
>>> rom and trap to KVM, then KVM can't find the corresponding memslot.
>>> While KVM (on ARM) injects an abort to guest due to the broken hva, then
>>> guest will get stuck.
>>>
>>> Signed-off-by: Shannon Zhao <address@hidden>
>>
>> I'm a bit worried about old_flags not being set on all paths to
>> kvm_set_user_memory_region.  This would lead to extra
>> KVM_SET_USER_MEMORY_REGION calls.  It should not be a problem but
>> it is ugly.  Does something like the additional changes below work for you?
>>
> I test below patch. It works for our testcase.
> Do I need to fold them into one and resend?

No need to, thanks!

Paolo