Re: [Xen-devel] [PATCH v2 1/3] x86 / vmx: make apic_access_mfn type-safe

["Durrant, Paul" <pdurrant@xxxxxxxxxxxx>]

> -----Original Message-----
> From: Xen-devel <xen-devel-bounces@xxxxxxxxxxxxxxxxxxxx> On Behalf Of Jan
> Beulich
> Sent: 23 January 2020 12:45
> To: Durrant, Paul <pdurrant@xxxxxxxxxxxx>
> Cc: Kevin Tian <kevin.tian@xxxxxxxxx>; Wei Liu <wl@xxxxxxx>; Andrew Cooper
> <andrew.cooper3@xxxxxxxxxx>; Jun Nakajima <jun.nakajima@xxxxxxxxx>; xen-
> devel@xxxxxxxxxxxxxxxxxxxx; Roger Pau Monné <roger.pau@xxxxxxxxxx>
> Subject: Re: [Xen-devel] [PATCH v2 1/3] x86 / vmx: make apic_access_mfn
> type-safe
> 
> On 23.01.2020 13:21, Paul Durrant wrote:
> > Use mfn_t rather than unsigned long and change previous tests against 0
> to
> > tests against INVALID_MFN (also introducing initialization to that
> value).
> >
> > Signed-off-by: Paul Durrant <pdurrant@xxxxxxxxxx>
> > Acked-by: Kevin Tian <kevin.tian@xxxxxxxxx>
> > Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
> 
> No, this isn't what the R-b was given for.

Oh, sorry, I misunderstood; I thought the R-b was good as long as idempotency 
was ensured.

> 
> > v2:
> >  - Set apic_access_mfn to INVALID_MFN in vmx_free_vlapic_mapping() to
> make
> >    the function idempotent
> 
> Andrew had suggested to use 0 instead of INVALID_MFN. I don't see
> how you achieved idempotency with this adjustment. Aiui
> vmx_free_vlapic_mapping() is supposed to also run correctly if
> vmx_alloc_vlapic_mapping() was never called.

It will. vmx_domain_initialise() will set apic_access_mfn to INVALID_MFN so 
vmx_free_vlapic_mapping() will do nothing.

  Paul
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