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SubjectRe: [PATCH 1/3] Implement emulator_write_phys()
Anthony Liguori wrote:
> On Mon, 2007-08-27 at 18:45 +0300, Avi Kivity wrote:
>
>> Anthony Liguori wrote:
>>
>>> Since a hypercall may span two pages and is a gva, we need a function to write
>>> to a gva that may span multiple pages. emulator_write_phys() seems like the
>>> logical choice for this.
>>>
>>> @@ -962,8 +962,35 @@ static int emulator_write_std(unsigned long addr,
>>> unsigned int bytes,
>>> struct kvm_vcpu *vcpu
>>>
>> I think that emulator_write_emulated(), except for being awkwardly
>> named, should do the job. We have enough APIs.
>>
>> But! We may not overwrite the hypercall instruction while a vcpu may be
>> executing, since there's no atomicity guarantee for code fetch. We have
>> to to be out of guest mode while writing that insn.
>>
>
>
> Hrm, good catch.
>
> How can we get out of guest mode given SMP guest support?
>
>

kvm_flush_remote_tlbs() is something that can be generalized.
Basically, you set a bit in each vcpu and send an IPI to take them out.

But that's deadlock prone and complex. Maybe you can just take
kvm->lock, zap the mmu and the flush tlbs, and patch the instruction at
your leisure, as no vcpu will be able to map memory until the lock is
released.

--
Any sufficiently difficult bug is indistinguishable from a feature.

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