Re: [Xen-devel] [PATCH v2 3/4] VMX: Assign the right value to 'NDST' field in a concern case

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 26.05.16 at 15:39, <feng.wu@xxxxxxxxx> wrote:
> Normally, in vmx_cpu_block() 'NDST' filed should have the same
> value with 'dest' or 'MASK_INSR(dest, PI_xAPIC_NDST_MASK)' depending
> on whether x2apic is enabled. However, in the following scenario,
> 'NDST' has different value:
> 
> 'vcpu_block' hook gets assigned in vmx_pi_hooks_assign(), but all
> other three PI hooks have not been assigned or not been excuted yet.
> And during this interval, we are running in vmx_vcpu_block(), then
> 'NDST' may have different value.

How about simply assigning vcpu_block last? Or alternatively
holding pi_blocking_list_lock around all four assignments? Or
(maybe in addition to one of these) writing something sensible in
vmx_pi_hooks_assign() before doing the hook assignments? Of
course much depends on whether the ASSERT() you replace was
meant just as a sanity check, or instead logic elsewhere relies on
NDST having the right value already before getting into
vmx_vcpu_block().

Also, rather than saying twice that NDST has a different value in
that case, how about stating what exact value it has then and
why that's not what we want/need? (Same goes for the code
comment then.)

> This patch fix this concern case.

Here as well as in earlier patches - do you perhaps mean "corner
case"?

Jan


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