Re: [Qemu-devel] [PATCH 4/6] i386: acpi: add IVHD device entry for IOAPIC

[Peter Xu]

On Wed, Sep 12, 2018 at 02:11:10PM -0500, Brijesh Singh wrote:
> 
> 
> On 09/11/2018 11:35 PM, Peter Xu wrote:
> > On Tue, Sep 11, 2018 at 11:49:47AM -0500, Brijesh Singh wrote:
> > > When interrupt remapping is enabled, add a special IVHD device
> > > (type IOAPIC) -- which is typically PCI device 14:0.0. Linux IOMMU driver
> > > checks for this special device.
> > > 
> > > 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 | 20 +++++++++++++++++++-
> > >   1 file changed, 19 insertions(+), 1 deletion(-)
> > > 
> > > diff --git a/hw/i386/acpi-build.c b/hw/i386/acpi-build.c
> > > index e1ee8ae..5c2c638 100644
> > > --- a/hw/i386/acpi-build.c
> > > +++ b/hw/i386/acpi-build.c
> > > @@ -2519,6 +2519,7 @@ build_dmar_q35(GArray *table_data, BIOSLinker 
> > > *linker)
> > >   static void
> > >   build_amd_iommu(GArray *table_data, BIOSLinker *linker)
> > >   {
> > > +    int ivhd_table_len = 28;
> > >       int iommu_start = table_data->len;
> > >       AMDVIState *s = AMD_IOMMU_DEVICE(x86_iommu_get_default());
> > > @@ -2540,8 +2541,16 @@ build_amd_iommu(GArray *table_data, BIOSLinker 
> > > *linker)
> > >                                (1UL << 6) | /* PrefSup      */
> > >                                (1UL << 7),  /* PPRSup       */
> > >                                1);
> > > +
> > > +    /*
> > > +     * When interrupt remapping is enabled, we add a special IVHD device
> > > +     * for type IO-APIC.
> > > +     */
> > > +    if (s->intr_enabled) {
> > > +        ivhd_table_len += 8;
> > > +    }
> > >       /* IVHD length */
> > > -    build_append_int_noprefix(table_data, 28, 2);
> > > +    build_append_int_noprefix(table_data, ivhd_table_len, 2);
> > >       /* DeviceID */
> > >       build_append_int_noprefix(table_data, s->devid, 2);
> > >       /* Capability offset */
> > > @@ -2565,6 +2574,15 @@ build_amd_iommu(GArray *table_data, BIOSLinker 
> > > *linker)
> > >        */
> > >       build_append_int_noprefix(table_data, 0x0000001, 4);
> > > +    /*
> > > +     * When interrupt remapping is enabled, Linux IOMMU driver also 
> > > checks
> > > +     * for special IVHD device (type IO-APIC), which is typically 
> > > presented
> > > +     * as PCI device 14:00.0.
> > > +     */
> > > +    if (s->intr_enabled) {
> > > +        build_append_int_noprefix(table_data, 0x0100a00000000048, 8);
> > 
> > Some comments on the bit definition would be nicer, or "please refer
> > to Table 95 of AMD-Vi spec".
> > 
> > Could I ask how come the 14:00.0?  Is that in the spec somewhere?
> > 
> > And since you explicitly mentioned Linux, then... would it work for
> > Windows too?
> > 
> 
> The PCI 14:00.0 is SouthBridge IOAPIC device. On bare metal the timer
> subsystem is connected to the SB IOAPIC. The IVRS table must contains
> the entry of SB IOAPIC otherwise Linux will not enable the IR mapping
> while parsing the IVRS.
> 
> On bare meta system, IVRS will always have entry for SB IOAPIC. As per
> Windows is concerned, I am not sure if Windows support interrupt remap.
> If it does, adding the SB IOAPIC devid should not cause any problem
> to it because its always available on bare metal system.
> 
> Here is linux commit
> 
> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=c2ff5cf5294bcbd7fa50f7d860e90a66db7e5059

Thanks for these information.  Please feel free to add some of the
information into the comment, that might explain itself better.  When
referring to commits, I would suggest just use "Please refer to Linux
commit xxx (xxx)" rather than the link though.

Regards,

-- 
Peter Xu