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
arch implements kvm_arch_register_noncoherent_dma().
Signed-off-by: Jason Gunthorpe <jgg@xxxxxxxxxx>
---
drivers/iommu/intel/iommu.c | 7 ++-----
drivers/vfio/vfio_iommu_type1.c | 30 +++++++++++++++++++-----------
include/linux/intel-iommu.h | 1 -
3 files changed, 21 insertions(+), 17 deletions(-)
diff --git a/drivers/iommu/intel/iommu.c b/drivers/iommu/intel/iommu.c
index f08611a6cc4799..8f3674e997df06 100644
--- a/drivers/iommu/intel/iommu.c
+++ b/drivers/iommu/intel/iommu.c
@@ -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->enforce_no_snoop)
+ if (dmar_domain->enforce_no_snoop)
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->enforce_no_snoop = true;
return true;
diff --git a/drivers/vfio/vfio_iommu_type1.c b/drivers/vfio/vfio_iommu_type1.c
index 9394aa9444c10c..c13b9290e35759 100644
--- a/drivers/vfio/vfio_iommu_type1.c
+++ b/drivers/vfio/vfio_iommu_type1.c
@@ -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;
}
diff --git a/include/linux/intel-iommu.h b/include/linux/intel-iommu.h
index 1f930c0c225d94..bc39f633efdf03 100644
--- a/include/linux/intel-iommu.h
+++ b/include/linux/intel-iommu.h
@@ -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 enforce_no_snoop : 1; /* Create IOPTEs with snoop control */
struct list_head devices; /* all devices' list */
--
2.35.1
