Re: [Xen-devel] [PATCH v2 1/2] VMX: fix VMCS race on context-switch paths

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 17.02.17 at 09:40, <sergey.dyasli@xxxxxxxxxx> wrote:
> On Thu, 2017-02-16 at 04:15 -0700, Jan Beulich wrote:
>> When __context_switch() is being bypassed during original context
>> switch handling, the vCPU "owning" the VMCS partially loses control of
>> it: It will appear non-running to remote CPUs, and hence their attempt
>> to pause the owning vCPU will have no effect on it (as it already
>> looks to be paused). At the same time the "owning" CPU will re-enable
>> interrupts eventually (the lastest when entering the idle loop) and
>> hence becomes subject to IPIs from other CPUs requesting access to the
>> VMCS. As a result, when __context_switch() finally gets run, the CPU
>> may no longer have the VMCS loaded, and hence any accesses to it would
>> fail. Hence we may need to re-load the VMCS in vmx_ctxt_switch_from().
>> 
>> Similarly, when __context_switch() is being bypassed also on the second
>> (switch-in) path, VMCS ownership may have been lost and hence needs
>> re-establishing. Since there's no existing hook to put this in, add a
>> new one.
> 
> This paragraph now has to be replaced with something about
> vmx_do_resume() change.

Oh, I had tried to remember to update this, but then forgot (ending
up mentioning this only in the v2 info). Thanks for noticing.

Jan


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