RE: [PATCH v2 1/3] x86/IOMMU: mark IOMMU / intremap not in use when ACPI tables are missing

["Tian, Kevin" <kevin.tian@intel.com>]

> From: Jan Beulich <jbeulich@suse.com>
> Sent: Friday, October 22, 2021 1:59 PM
> 
> On 21.10.2021 11:58, Jan Beulich wrote:
> > x2apic_bsp_setup() gets called ahead of iommu_setup(), and since x2APIC
> > mode (physical vs clustered) depends on iommu_intremap, that variable
> > needs to be set to off as soon as we know we can't / won't enable
> > interrupt remapping, i.e. in particular when parsing of the respective
> > ACPI tables failed. Move the turning off of iommu_intremap from AMD
> > specific code into acpi_iommu_init(), accompanying it by clearing of
> > iommu_enable.
> >
> > Take the opportunity and also fully skip ACPI table parsing logic on
> > VT-d when both "iommu=off" and "iommu=no-intremap" are in effect
> anyway,
> > like was already the case for AMD.
> >
> > The tag below only references the commit uncovering a pre-existing
> > anomaly.
> >
> > Fixes: d8bd82327b0f ("AMD/IOMMU: obtain IVHD type to use earlier")
> > Reported-by: Andrew Cooper <andrew.cooper3@citrix.com>
> > Signed-off-by: Jan Beulich <jbeulich@suse.com>
> 
> Ouch, forgot to Cc Kevin; now added.

Reviewed-by: Kevin Tian <kevin.tian@intel.com>

> 
> Jan
> 
> > ---
> > While the change here deals with apic_x2apic_probe() as called from
> > x2apic_bsp_setup(), the check_x2apic_preenabled() path looks to be
> > similarly affected. That call occurs before acpi_boot_init(), which is
> > what calls acpi_iommu_init(). The ordering in setup.c is in part
> > relatively fragile, which is why for the moment I'm still hesitant to
> > move the generic_apic_probe() call down. Plus I don't have easy access
> > to a suitable system to test this case. Thoughts?
> > ---
> > v2: Treat iommu_enable and iommu_intremap as separate options.
> >
> > --- a/xen/drivers/passthrough/amd/pci_amd_iommu.c
> > +++ b/xen/drivers/passthrough/amd/pci_amd_iommu.c
> > @@ -183,9 +183,6 @@ int __init acpi_ivrs_init(void)
> >  {
> >      int rc;
> >
> > -    if ( !iommu_enable && !iommu_intremap )
> > -        return 0;
> > -
> >      rc = amd_iommu_get_supported_ivhd_type();
> >      if ( rc < 0 )
> >          return rc;
> > @@ -193,10 +190,7 @@ int __init acpi_ivrs_init(void)
> >      ivhd_type = rc;
> >
> >      if ( (amd_iommu_detect_acpi() !=0) || (iommu_found() == 0) )
> > -    {
> > -        iommu_intremap = iommu_intremap_off;
> >          return -ENODEV;
> > -    }
> >
> >      iommu_init_ops = &_iommu_init_ops;
> >
> > --- a/xen/drivers/passthrough/vtd/dmar.c
> > +++ b/xen/drivers/passthrough/vtd/dmar.c
> > @@ -777,11 +777,7 @@ static int __init acpi_parse_dmar(struct
> >      dmar = (struct acpi_table_dmar *)table;
> >      dmar_flags = dmar->flags;
> >
> > -    if ( !iommu_enable && !iommu_intremap )
> > -    {
> > -        ret = -EINVAL;
> > -        goto out;
> > -    }
> > +    ASSERT(iommu_enable || iommu_intremap);
> >
> >      if ( !dmar->width )
> >      {
> > --- a/xen/drivers/passthrough/x86/iommu.c
> > +++ b/xen/drivers/passthrough/x86/iommu.c
> > @@ -41,6 +41,24 @@ enum iommu_intremap __read_mostly iommu_
> >  bool __read_mostly iommu_intpost;
> >  #endif
> >
> > +void __init acpi_iommu_init(void)
> > +{
> > +    int ret;
> > +
> > +    if ( !iommu_enable && !iommu_intremap )
> > +        return;
> > +
> > +    ret = acpi_dmar_init();
> > +    if ( ret == -ENODEV )
> > +        ret = acpi_ivrs_init();
> > +
> > +    if ( ret )
> > +    {
> > +        iommu_enable = false;
> > +        iommu_intremap = iommu_intremap_off;
> > +    }
> > +}
> > +
> >  int __init iommu_hardware_setup(void)
> >  {
> >      struct IO_APIC_route_entry **ioapic_entries = NULL;
> > --- a/xen/include/asm-x86/acpi.h
> > +++ b/xen/include/asm-x86/acpi.h
> > @@ -141,16 +141,10 @@ extern u32 x86_acpiid_to_apicid[];
> >  extern u32 pmtmr_ioport;
> >  extern unsigned int pmtmr_width;
> >
> > +void acpi_iommu_init(void);
> >  int acpi_dmar_init(void);
> >  int acpi_ivrs_init(void);
> >
> > -static inline int acpi_iommu_init(void)
> > -{
> > -    int ret = acpi_dmar_init();
> > -
> > -    return ret == -ENODEV ? acpi_ivrs_init() : ret;
> > -}
> > -
> >  void acpi_mmcfg_init(void);
> >
> >  /* Incremented whenever we transition through S3. Value is 1 during boot.
> */
> >
> >