Re: [Xen-devel] [PATCH] Re: I/O port access handling for PVH

[George Dunlap <george.dunlap@xxxxxxxxxxxxx>]

On 11/28/2013 11:01 AM, Tim Deegan wrote:
> At 15:10 +0100 on 21 Oct (1382364606), Jan Beulich wrote:
> > In particular it would then hopefully be safe to do all that without
> > the on-stack emulation stub, as this ought to be necessary only
> > for Dom0, which ought to always have direct access to such
> > "special" I/O ports. With one apparent caveat: SVM sets
> > GENERAL1_INTERCEPT_SMI (for a reason that escapes my right
> > now), and hence control doesn't transfer directly to SMM when
> > an SMI occurs (and consequently registers aren't expected). But
> > I would hope that this intercept isn't really needed, and hence
> > could be dropped at least for PVH guests.
> (I realise I'm rather late replying to this - I put it aside and then
> only found it again today)
>
> On machines where the BIOS has locked down SMM mode, this
> intercept is in fact ignored by the hardware, and that works fine.
> So we can drop it for all VMs if it's convenient:
>
> commit a842864f3901078e2a5f4d1cca2f01a72c8d7d13
> Author: Tim Deegan <tim@xxxxxxx>
> Date:   Thu Nov 28 10:58:42 2013 +0000
>
>      x86/svm: don't intercept SMI.
>      
>      The SMI intercept is ignored anyway when the BIOS has set the SMMLOCK
>      bit in HWCR (see APM v3.21, volume 2, 15.13.3) and it's convenient for
>      PVH IO processing to have the SMI handled directly with the guest's
>      GPR state (for BIOSes that use SMI as a sort of function call interface).
>      
>      Signed-off-by: Tim Deegan <tim@xxxxxxx>
I take it you're not targeting this for 4.4?

 -George

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