Re: [Qemu-devel] [PATCH 6/6] x86_iommu/amd: Enable Guest virtual APIC support

[Suravee Suthikulpanit]

Peter,

On 9/12/18 11:52 AM, Peter Xu wrote:
> On Tue, Sep 11, 2018 at 11:49:49AM -0500, Brijesh Singh wrote:
> > Now that amd-iommu support interrupt remapping, enable the GASup in IVRS
> > table and GASup in extended feature register to indicate that IOMMU
> > support guest virtual APIC mode.
> >
> > Note that the GAMSup is set to zero to indicate that  Guest Virtual
> > APIC does not support advanced interrupt features (i.e virtualized
> > interrupts using the guest virtual APIC).
> >
> > See Table 21 from IOMMU spec for interrupt virtualization controls
> >
> > IOMMU spec: https://support.amd.com/TechDocs/48882_IOMMU.pdf
> >
> > Cc: "Michael S. Tsirkin" <address@hidden>
> > Cc: Paolo Bonzini <address@hidden>
> > Cc: Richard Henderson <address@hidden>
> > Cc: Eduardo Habkost <address@hidden>
> > Cc: Marcel Apfelbaum <address@hidden>
> > Cc: Tom Lendacky <address@hidden>
> > Cc: Suravee Suthikulpanit <address@hidden>
> > Signed-off-by: Brijesh Singh <address@hidden>
> > ---
> >   hw/i386/acpi-build.c | 3 ++-
> >   hw/i386/amd_iommu.h  | 2 +-
> >   2 files changed, 3 insertions(+), 2 deletions(-)
> >
> > diff --git a/hw/i386/acpi-build.c b/hw/i386/acpi-build.c
> > index 5c2c638..1cbc8ba 100644
> > --- a/hw/i386/acpi-build.c
> > +++ b/hw/i386/acpi-build.c
> > @@ -2565,7 +2565,8 @@ build_amd_iommu(GArray *table_data, BIOSLinker *linker)
> >       build_append_int_noprefix(table_data,
> >                                (48UL << 30) | /* HATS   */
> >                                (48UL << 28) | /* GATS   */
> > -                             (1UL << 2),    /* GTSup  */
> > +                             (1UL << 2)   | /* GTSup  */
> > +                             (1UL << 6),    /* GASup  */
>
> Sorry if I misunderstood - is this for nested?
>
> I'm a bit confused here... IIUC in your previous patches you didn't
> really implement guest_mode==1 case in IRTEs.  So if you have this set
> then the guest should be able to setup IRTEs with guest_mode==1?  How
> did it work?
>
> Thanks,

The naming of these bits are confusing. Please allow me to help explain.
There are two capability bits:

* GASup  : This is to allow 128-bit IRTE when GAEn is set.

* GAMSup : This is for Guest Virtual APIC mode support,
            which is not currently supported in vIOMMU.
           The commit message in patch 5 is incorrect.

Here, we set GASup in order to allow 128-bit IRTE support,
which is needed for some of future AMD IOMMU features.

Thanks,
Suravee