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vfio: Move the Intel no-snoop control off of IOMMU_CACHE 

IOMMU_CACHE means "normal DMA to this iommu_domain's IOVA should be cache
coherent" and is used by the DMA API. The definition allows for special
non-coherent DMA to exist - ie processing of the no-snoop flag in PCIe
TLPs - so long as this behavior is opt-in by the device driver.

The flag is mainly used by the DMA API to synchronize the IOMMU setting
with the expected cache behavior of the DMA master. eg based on
dev_is_dma_coherent() in some case.

For Intel IOMMU IOMMU_CACHE was redefined to mean 'force all DMA to be
cache coherent' which has the practical effect of causing the IOMMU to
ignore the no-snoop bit in a PCIe TLP.

x86 platforms are always IOMMU_CACHE, so Intel should ignore this flag.

Instead use the new domain op enforce_cache_coherency() which causes every
IOPTE created in the domain to have the no-snoop blocking behavior.

Reconfigure VFIO to always use IOMMU_CACHE and call
enforce_cache_coherency() to operate the special Intel behavior.

Remove the IOMMU_CACHE test from Intel IOMMU.

Ultimately VFIO plumbs the result of enforce_cache_coherency() back into
the x86 platform code through kvm_arch_register_noncoherent_dma() which
controls if the WBINVD instruction is available in the guest.  No other
archs implement kvm_arch_register_noncoherent_dma() nor are there any
other known consumers of VFIO_DMA_CC_IOMMU that might be affected by the
user visible result change on non-x86 archs.

Reviewed-by: Kevin Tian <kevin.tian@intel.com>
Reviewed-by: Lu Baolu <baolu.lu@linux.intel.com>
Acked-by: Alex Williamson <alex.williamson@redhat.com>
Acked-by: Robin Murphy <robin.murphy@arm.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>
Link: https://lore.kernel.org/r/2-v3-2cf356649677+a32-intel_no_snoop_jgg@nvidia.com
Signed-off-by: Joerg Roedel <jroedel@suse.de>
This commit is contained in:
Jason Gunthorpe 2022-04-11 12:16:06 -03:00 committed by Joerg Roedel
parent 6043257b1d
commit 71cfafda9c
3 changed files with 21 additions and 17 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

7
drivers/iommu/intel/iommu.c
View File

@ -641,7 +641,6 @@ static unsigned long domain_super_pgsize_bitmap(struct dmar_domain *domain)
static void domain_update_iommu_cap(struct dmar_domain *domain)
{
domain_update_iommu_coherency(domain);
domain->iommu_snooping = domain_update_iommu_snooping(NULL);
domain->iommu_superpage = domain_update_iommu_superpage(domain, NULL);
/*
@ -4283,7 +4282,6 @@ static int md_domain_init(struct dmar_domain *domain, int guest_width)
domain->agaw = width_to_agaw(adjust_width);
domain->iommu_coherency = false;
domain->iommu_snooping = false;
domain->iommu_superpage = 0;
domain->max_addr = 0;
@ -4422,8 +4420,7 @@ static int intel_iommu_map(struct iommu_domain *domain,
prot |= DMA_PTE_READ;
if (iommu_prot & IOMMU_WRITE)
prot |= DMA_PTE_WRITE;
if (((iommu_prot & IOMMU_CACHE) && dmar_domain->iommu_snooping) ||
dmar_domain->force_snooping)
if (dmar_domain->force_snooping)
prot |= DMA_PTE_SNP;
max_addr = iova + size;
@ -4550,7 +4547,7 @@ static bool intel_iommu_enforce_cache_coherency(struct iommu_domain *domain)
{
struct dmar_domain *dmar_domain = to_dmar_domain(domain);
if (!dmar_domain->iommu_snooping)
if (!domain_update_iommu_snooping(NULL))
return false;
dmar_domain->force_snooping = true;
return true;

30
drivers/vfio/vfio_iommu_type1.c
View File

@ -84,8 +84,8 @@ struct vfio_domain {
struct iommu_domain *domain;
struct list_head next;
struct list_head group_list;
int prot; /* IOMMU_CACHE */
bool fgsp; /* Fine-grained super pages */
bool fgsp : 1; /* Fine-grained super pages */
bool enforce_cache_coherency : 1;
};
struct vfio_dma {
@ -1461,7 +1461,7 @@ static int vfio_iommu_map(struct vfio_iommu *iommu, dma_addr_t iova,
list_for_each_entry(d, &iommu->domain_list, next) {
ret = iommu_map(d->domain, iova, (phys_addr_t)pfn << PAGE_SHIFT,
npage << PAGE_SHIFT, prot | d->prot);
npage << PAGE_SHIFT, prot | IOMMU_CACHE);
if (ret)
goto unwind;
@ -1771,7 +1771,7 @@ static int vfio_iommu_replay(struct vfio_iommu *iommu,
}
ret = iommu_map(domain->domain, iova, phys,
size, dma->prot | domain->prot);
size, dma->prot | IOMMU_CACHE);
if (ret) {
if (!dma->iommu_mapped) {
vfio_unpin_pages_remote(dma, iova,
@ -1859,7 +1859,7 @@ static void vfio_test_domain_fgsp(struct vfio_domain *domain)
return;
ret = iommu_map(domain->domain, 0, page_to_phys(pages), PAGE_SIZE * 2,
IOMMU_READ | IOMMU_WRITE | domain->prot);
IOMMU_READ | IOMMU_WRITE | IOMMU_CACHE);
if (!ret) {
size_t unmapped = iommu_unmap(domain->domain, 0, PAGE_SIZE);
@ -2267,8 +2267,15 @@ static int vfio_iommu_type1_attach_group(void *iommu_data,
goto out_detach;
}
if (iommu_capable(bus, IOMMU_CAP_CACHE_COHERENCY))
domain->prot |= IOMMU_CACHE;
/*
* If the IOMMU can block non-coherent operations (ie PCIe TLPs with
* no-snoop set) then VFIO always turns this feature on because on Intel
* platforms it optimizes KVM to disable wbinvd emulation.
*/
if (domain->domain->ops->enforce_cache_coherency)
domain->enforce_cache_coherency =
domain->domain->ops->enforce_cache_coherency(
domain->domain);
/*
* Try to match an existing compatible domain. We don't want to
@ -2279,7 +2286,8 @@ static int vfio_iommu_type1_attach_group(void *iommu_data,
*/
list_for_each_entry(d, &iommu->domain_list, next) {
if (d->domain->ops == domain->domain->ops &&
d->prot == domain->prot) {
d->enforce_cache_coherency ==
domain->enforce_cache_coherency) {
iommu_detach_group(domain->domain, group->iommu_group);
if (!iommu_attach_group(d->domain,
group->iommu_group)) {
@ -2611,14 +2619,14 @@ static void vfio_iommu_type1_release(void *iommu_data)
kfree(iommu);
}
static int vfio_domains_have_iommu_cache(struct vfio_iommu *iommu)
static int vfio_domains_have_enforce_cache_coherency(struct vfio_iommu *iommu)
{
struct vfio_domain *domain;
int ret = 1;
mutex_lock(&iommu->lock);
list_for_each_entry(domain, &iommu->domain_list, next) {
if (!(domain->prot & IOMMU_CACHE)) {
if (!(domain->enforce_cache_coherency)) {
ret = 0;
break;
}
@ -2641,7 +2649,7 @@ static int vfio_iommu_type1_check_extension(struct vfio_iommu *iommu,
case VFIO_DMA_CC_IOMMU:
if (!iommu)
return 0;
return vfio_domains_have_iommu_cache(iommu);
return vfio_domains_have_enforce_cache_coherency(iommu);
default:
return 0;
}

1
include/linux/intel-iommu.h
View File

@ -539,7 +539,6 @@ struct dmar_domain {
u8 has_iotlb_device: 1;
u8 iommu_coherency: 1; /* indicate coherency of iommu access */
u8 iommu_snooping: 1; /* indicate snooping control feature */
u8 force_snooping : 1; /* Create IOPTEs with snoop control */
struct list_head devices; /* all devices' list */