RE: [PATCH 1/2] VT-d: install sync_cache hook on demand

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

> From: Jan Beulich <jbeulich@suse.com>
> Sent: Wednesday, July 15, 2020 6:04 PM
> 
> Instead of checking inside the hook whether any non-coherent IOMMUs are
> present, simply install the hook only when this is the case.
> 
> To prove that there are no other references to the now dynamically
> updated ops structure (and hence that its updating happens early
> enough), make it static and rename it at the same time.
> 
> Note that this change implies that sync_cache() shouldn't be called
> directly unless there are unusual circumstances, like is the case in
> alloc_pgtable_maddr(), which gets invoked too early for iommu_ops to
> be set already (and therefore we also need to be careful there to
> avoid accessing vtd_ops later on, as it lives in .init).
> 
> Signed-off-by: Jan Beulich <jbeulich@suse.com>

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

> 
> --- a/xen/drivers/passthrough/vtd/extern.h
> +++ b/xen/drivers/passthrough/vtd/extern.h
> @@ -28,7 +28,6 @@
>  struct pci_ats_dev;
>  extern bool_t rwbf_quirk;
>  extern const struct iommu_init_ops intel_iommu_init_ops;
> -extern const struct iommu_ops intel_iommu_ops;
> 
>  void print_iommu_regs(struct acpi_drhd_unit *drhd);
>  void print_vtd_entries(struct vtd_iommu *iommu, int bus, int devfn, u64
> gmfn);
> --- a/xen/drivers/passthrough/vtd/iommu.c
> +++ b/xen/drivers/passthrough/vtd/iommu.c
> @@ -59,6 +59,7 @@ bool __read_mostly iommu_snoop = true;
> 
>  int nr_iommus;
> 
> +static struct iommu_ops vtd_ops;
>  static struct tasklet vtd_fault_tasklet;
> 
>  static int setup_hwdom_device(u8 devfn, struct pci_dev *);
> @@ -146,16 +147,11 @@ static int context_get_domain_id(struct
>      return domid;
>  }
> 
> -static int iommus_incoherent;
> -
>  static void sync_cache(const void *addr, unsigned int size)
>  {
>      static unsigned long clflush_size = 0;
>      const void *end = addr + size;
> 
> -    if ( !iommus_incoherent )
> -        return;
> -
>      if ( clflush_size == 0 )
>          clflush_size = get_cache_line_size();
> 
> @@ -217,7 +213,8 @@ uint64_t alloc_pgtable_maddr(unsigned lo
>          vaddr = __map_domain_page(cur_pg);
>          memset(vaddr, 0, PAGE_SIZE);
> 
> -        sync_cache(vaddr, PAGE_SIZE);
> +        if ( (iommu_ops.init ? &iommu_ops : &vtd_ops)->sync_cache )
> +            sync_cache(vaddr, PAGE_SIZE);
>          unmap_domain_page(vaddr);
>          cur_pg++;
>      }
> @@ -1227,7 +1224,7 @@ int __init iommu_alloc(struct acpi_drhd_
>      iommu->nr_pt_levels = agaw_to_level(agaw);
> 
>      if ( !ecap_coherent(iommu->ecap) )
> -        iommus_incoherent = 1;
> +        vtd_ops.sync_cache = sync_cache;
> 
>      /* allocate domain id bitmap */
>      nr_dom = cap_ndoms(iommu->cap);
> @@ -2737,7 +2734,7 @@ static int __init intel_iommu_quarantine
>      return level ? -ENOMEM : rc;
>  }
> 
> -const struct iommu_ops __initconstrel intel_iommu_ops = {
> +static struct iommu_ops __initdata vtd_ops = {
>      .init = intel_iommu_domain_init,
>      .hwdom_init = intel_iommu_hwdom_init,
>      .quarantine_init = intel_iommu_quarantine_init,
> @@ -2768,11 +2765,10 @@ const struct iommu_ops __initconstrel in
>      .iotlb_flush_all = iommu_flush_iotlb_all,
>      .get_reserved_device_memory =
> intel_iommu_get_reserved_device_memory,
>      .dump_p2m_table = vtd_dump_p2m_table,
> -    .sync_cache = sync_cache,
>  };
> 
>  const struct iommu_init_ops __initconstrel intel_iommu_init_ops = {
> -    .ops = &intel_iommu_ops,
> +    .ops = &vtd_ops,
>      .setup = vtd_setup,
>      .supports_x2apic = intel_iommu_supports_eim,
>  };