Re: [Xen-devel] [PATCH] x86/vtsc: update vcpu_time after hvm_set_guest_time

[George Dunlap <george.dunlap@xxxxxxxxxxxxx>]

On 06/04/2013 10:10 AM, Roger Pau Monne wrote:
> When using a vtsc, hvm_set_guest_time changes hvm_vcpu.stime_offset,
> which is used in the vcpu time structure to calculate the
> tsc_timestamp, so after updating stime_offset we need to propagate the
> change to vcpu_time in order for the guest to get the right time if
> using the PV clock.
>
> This was not done correctly, since in context_switch
> update_vcpu_system_time was called before vmx_do_resume, which caused
> the vcpu_info time structure to be updated with the wrong values. This
> patch fixes this by calling update_vcpu_system_time after the call to
> hvm_set_guest_time has happened.
Would it make more sense to actually do this in hvm_set_guest_time() 
instead, so that this window where the vcpu system_time is closed for 
all callers, not just hvm_do_resume?
You could gate calling update_vcpu_system_time on:
1. Whether stime_offset actually changed
2. Whether v is currently running

 -George


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