Re: [PATCH v3 18/22] amd_iommu: Toggle address translation mode on devtab entry invalidation

["Michael S. Tsirkin" <mst@redhat.com>]

On Mon, Oct 06, 2025 at 11:38:28AM +0530, Sairaj Kodilkar wrote:
> 
> 
> On 9/20/2025 3:05 AM, Alejandro Jimenez wrote:
> > A guest must issue an INVALIDATE_DEVTAB_ENTRY command after changing a
> > Device Table entry (DTE) e.g. after attaching a device and setting up its
> > DTE. When intercepting this event, determine if the DTE has been configured
> > for paging or not, and toggle the appropriate memory regions to allow DMA
> > address translation for the address space if needed. Requires dma-remap=on.
> > 
> > Signed-off-by: Alejandro Jimenez <alejandro.j.jimenez@oracle.com>
> > ---
> >   hw/i386/amd_iommu.c | 122 +++++++++++++++++++++++++++++++++++++++++++-
> >   1 file changed, 120 insertions(+), 2 deletions(-)
> > 
> > diff --git a/hw/i386/amd_iommu.c b/hw/i386/amd_iommu.c
> > index ce5d4c36624fd..e916dcb2be381 100644
> > --- a/hw/i386/amd_iommu.c
> > +++ b/hw/i386/amd_iommu.c
> > @@ -1032,18 +1032,136 @@ static void amdvi_reset_address_translation_all(AMDVIState *s)
> >       }
> >   }
> > +static void enable_dma_mode(AMDVIAddressSpace *as, bool inval_current)
> > +{
> > +    /*
> > +     * When enabling DMA mode for the purpose of isolating guest devices on
> > +     * a failure to retrieve or invalid DTE, all existing mappings must be
> > +     * dropped.
> > +     */
> > +    if (inval_current) {
> > +        IOMMUNotifier *n;
> > +        IOMMU_NOTIFIER_FOREACH(n, &as->iommu) {
> > +            amdvi_address_space_unmap(as, n);
> > +        }
> > +    }
> > +
> > +    if (as->addr_translation) {
> > +        return;
> > +    }
> > +
> > +    /* Installing DTE enabling translation, activate region */
> > +    as->addr_translation = true;
> > +    amdvi_switch_address_space(as);
> > +    /* Sync shadow page tables */
> > +    amdvi_address_space_sync(as);
> Hi Alejandro,
> I think we can skip amdvi_address_space_sync, because
> amdvi_switch_address_space will trigger
> amdvi_iommu_replay. this replay should unmap all the old mappings and sync
> shadow page table.
> 
> Thanks
> Sairaj

Well I queued this but this speedup can be done on top.

-- 
MST