Re: [Xen-devel] [PATCH] x86/hvm/viridian: stop open coding updates to APIC registers

[Paul Durrant <Paul.Durrant@xxxxxxxxxx>]

> -----Original Message-----
> From: Jan Beulich [mailto:JBeulich@xxxxxxxx]
> Sent: 10 December 2018 13:44
> To: Paul Durrant <Paul.Durrant@xxxxxxxxxx>
> Cc: Andrew Cooper <Andrew.Cooper3@xxxxxxxxxx>; Roger Pau Monne
> <roger.pau@xxxxxxxxxx>; Wei Liu <wei.liu2@xxxxxxxxxx>; xen-devel <xen-
> devel@xxxxxxxxxxxxxxxxxxxx>
> Subject: Re: [PATCH] x86/hvm/viridian: stop open coding updates to APIC
> registers
> 
> >>> On 07.12.18 at 18:50, <paul.durrant@xxxxxxxxxx> wrote:
> > The code in viridian_synic_wrmsr() duplicates logic in
> vlapic_reg_write()
> > to update the ICR, ICR2 and TASKPRI registers. Instead of doing this,
> > make vlapic_reg_write() non-static and call it.
> 
> There's a side effect from this change, which I think should be called
> out since perhaps it's actually a (minor) bug fix: vlapic_reg_write()
> clears out vlapic->loaded, which the open coded Viridian code didn't
> do.
> 

Yes, that was an anomaly and did look wrong.

> If it wasn't for this, I would have been uncertain whether exposing a
> function that really was meant to be vlapic.c-internal is a good idea.
> 

Unfortunately the way that Microsoft specify the SynIC (as a "superset of the 
local APIC") means that the code does need to be closely tied. Do you want me 
to formulate a comment and submit a v2, or are you happy to add a comment on 
commit?

  Paul

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