[PATCH v8 05/10] iommu/amd: Introduce helper function to update 256-bit DTE

Suravee Suthikulpanit
2024-10-31T18:43:22Z

The current implementation does not follow 128-bit write requirement
to update DTE as specified in the AMD I/O Virtualization Techonology
(IOMMU) Specification.

Therefore, modify the struct dev_table_entry to contain union of u128 data
array, and introduce a helper functions update_dte256() to update DTE using
two 128-bit cmpxchg operations to update 256-bit DTE with the modified
structure, and take into account the DTE[V, GV] bits when programming
the DTE to ensure proper order of DTE programming and flushing.

In addition, introduce a per-DTE spin_lock struct dev_data.dte_lock to
provide synchronization when updating the DTE to prevent cmpxchg128
failure.

Suggested-by: Jason Gunthorpe <jgg@nvidia.com>
Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>
Signed-off-by: Suravee Suthikulpanit <suravee.suthikulpanit@amd.com>
---
drivers/iommu/amd/amd_iommu_types.h | 10 ++-
drivers/iommu/amd/iommu.c | 116 ++++++++++++++++++++++++++++
2 files changed, 125 insertions(+), 1 deletion(-)

diff --git a/drivers/iommu/amd/amd_iommu_types.h b/drivers/iommu/amd/amd_iommu_types.h
index 1e4ad1b247f5..8e5fbd78c302 100644
--- a/drivers/iommu/amd/amd_iommu_types.h
+++ b/drivers/iommu/amd/amd_iommu_types.h
@@ -427,9 +427,13 @@
#define DTE_GCR3_SHIFT_C 43

#define DTE_GPT_LEVEL_SHIFT 54
+#define DTE_GPT_LEVEL_MASK GENMASK_ULL(55, 54)

#define GCR3_VALID 0x01ULL

+/* DTE[128:179] | DTE[184:191] */
+#define DTE_DATA2_INTR_MASK ~GENMASK_ULL(55, 52)
+
#define IOMMU_PAGE_MASK (((1ULL << 52) - 1) & ~0xfffULL)
#define IOMMU_PTE_PRESENT(pte) ((pte) & IOMMU_PTE_PR)
#define IOMMU_PTE_DIRTY(pte) ((pte) & IOMMU_PTE_HD)
@@ -837,6 +841,7 @@ struct devid_map {
struct iommu_dev_data {
/*Protect against attach/detach races */
spinlock_t lock;
+ spinlock_t dte_lock; /* DTE lock for 256-bit access */

struct list_head list; /* For domain->dev_list */
struct llist_node dev_data_list; /* For global dev_data_list */
@@ -887,7 +892,10 @@ extern struct amd_iommu *amd_iommus[MAX_IOMMUS];
* Structure defining one entry in the device table
*/
struct dev_table_entry {
- u64 data[4];
+ union {
+ u64 data[4];
+ u128 data128[2];
+ };
};

/*
diff --git a/drivers/iommu/amd/iommu.c b/drivers/iommu/amd/iommu.c
index 8364cd6fa47d..eb22ed1a219c 100644
--- a/drivers/iommu/amd/iommu.c
+++ b/drivers/iommu/amd/iommu.c
@@ -77,12 +77,118 @@ static void detach_device(struct device *dev);
static void set_dte_entry(struct amd_iommu *iommu,
struct iommu_dev_data *dev_data);

+static void iommu_flush_dte_sync(struct amd_iommu *iommu, u16 devid);
+
/****************************************************************************
*
* Helper functions
*
****************************************************************************/

+static void write_dte_upper128(struct dev_table_entry *ptr, struct dev_table_entry *new)
+{
+ struct dev_table_entry old = {};
+
+ old.data128[1] = READ_ONCE(ptr->data128[1]);
+ do {
+ /*
+ * Preserve DTE_DATA2_INTR_MASK. This needs to be
+ * done here since it requires to be inside
+ * spin_lock(&dev_data->dte_lock) context.
+ */
+ new->data[2] &= ~DTE_DATA2_INTR_MASK;
+ new->data[2] |= old.data[2] & DTE_DATA2_INTR_MASK;
+
+ /* Note: try_cmpxchg inherently update &old.data128[1] on failure */
+ } while (!try_cmpxchg128(&ptr->data128[1], &old.data128[1], new->data128[1]));
+}
+
+static void write_dte_lower128(struct dev_table_entry *ptr, struct dev_table_entry *new)
+{
+ struct dev_table_entry old = {};
+
+ old.data128[0] = READ_ONCE(ptr->data128[0]);
+ do {
+ /* Note: try_cmpxchg inherently update &old.data128[0] on failure */
+ } while (!try_cmpxchg128(&ptr->data128[0], &old.data128[0], new->data128[0]));
+}
+
+/*
+ * Note:
+ * IOMMU reads the entire Device Table entry in a single 256-bit transaction
+ * but the driver is programming DTE using 2 128-bit cmpxchg. So, the driver
+ * need to ensure the following:
+ * - DTE[V|GV] bit is being written last when setting.
+ * - DTE[V|GV] bit is being written first when clearing.
+ *
+ * This function is used only by code, which updates DMA translation part of the DTE.
+ * So, only consider control bits related to DMA when updating the entry.
+ */
+static void update_dte256(struct amd_iommu *iommu, struct iommu_dev_data *dev_data,
+ struct dev_table_entry *new)
+{
+ struct dev_table_entry *dev_table = get_dev_table(iommu);
+ struct dev_table_entry *ptr = &dev_table[dev_data->devid];
+
+ spin_lock(&dev_data->dte_lock);
+
+ if (!(ptr->data[0] & DTE_FLAG_V)) {
+ /* Existing DTE is not valid. */
+ write_dte_upper128(ptr, new);
+ write_dte_lower128(ptr, new);
+ iommu_flush_dte_sync(iommu, dev_data->devid);
+ } else if (!(new->data[0] & DTE_FLAG_V)) {
+ /* Existing DTE is valid. New DTE is not valid. */
+ write_dte_lower128(ptr, new);
+ write_dte_upper128(ptr, new);
+ iommu_flush_dte_sync(iommu, dev_data->devid);
+ } else if (!FIELD_GET(DTE_FLAG_GV, ptr->data[0])) {
+ /*
+ * Both DTEs are valid.
+ * Existing DTE has no guest page table.
+ */
+ write_dte_upper128(ptr, new);
+ write_dte_lower128(ptr, new);
+ iommu_flush_dte_sync(iommu, dev_data->devid);
+ } else if (!FIELD_GET(DTE_FLAG_GV, new->data[0])) {
+ /*
+ * Both DTEs are valid.
+ * Existing DTE has guest page table,
+ * new DTE has no guest page table,
+ */
+ write_dte_lower128(ptr, new);
+ write_dte_upper128(ptr, new);
+ iommu_flush_dte_sync(iommu, dev_data->devid);
+ } else if (FIELD_GET(DTE_GPT_LEVEL_MASK, ptr->data[2]) !=
+ FIELD_GET(DTE_GPT_LEVEL_MASK, new->data[2])) {
+ /*
+ * Both DTEs are valid and have guest page table,
+ * but have different number of levels. So, we need
+ * to upadte both upper and lower 128-bit value, which
+ * require disabling and flushing.
+ */
+ struct dev_table_entry clear = {};
+
+ /* First disable DTE */
+ write_dte_lower128(ptr, &clear);
+ iommu_flush_dte_sync(iommu, dev_data->devid);
+
+ /* Then update DTE */
+ write_dte_upper128(ptr, new);
+ write_dte_lower128(ptr, new);
+ iommu_flush_dte_sync(iommu, dev_data->devid);
+ } else {
+ /*
+ * Both DTEs are valid and have guest page table,
+ * and same number of levels. We just need to only
+ * update the lower 128-bit. So no need to disable DTE.
+ */
+ write_dte_lower128(ptr, new);
+ }
+
+ spin_unlock(&dev_data->dte_lock);
+}
+
static inline bool pdom_is_v2_pgtbl_mode(struct protection_domain *pdom)
{
return (pdom && (pdom->pd_mode == PD_MODE_V2));
@@ -203,6 +309,7 @@ static struct iommu_dev_data *alloc_dev_data(struct amd_iommu *iommu, u16 devid)
return NULL;

spin_lock_init(&dev_data->lock);
+ spin_lock_init(&dev_data->dte_lock);
dev_data->devid = devid;
ratelimit_default_init(&dev_data->rs);

@@ -1272,6 +1379,15 @@ static int iommu_flush_dte(struct amd_iommu *iommu, u16 devid)
return iommu_queue_command(iommu, &cmd);
}

+static void iommu_flush_dte_sync(struct amd_iommu *iommu, u16 devid)
+{
+ int ret;
+
+ ret = iommu_flush_dte(iommu, devid);
+ if (!ret)
+ iommu_completion_wait(iommu);
+}
+
static void amd_iommu_flush_dte_all(struct amd_iommu *iommu)
{
u32 devid;
--
2.34.1