linux-kernel - [PATCH v2 1/3] iommu: amd: Use 4K page for completion wait write-back semaphore

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Date:   Wed, 23 Sep 2020 12:13:45 +0000
From:   Suravee Suthikulpanit <suravee.suthikulpanit@....com>
To:     linux-kernel@...r.kernel.org, iommu@...ts.linux-foundation.org
Cc:     joro@...tes.org, Jon.Grimm@....com, brijesh.singh@....com,
        Suravee Suthikulpanit <suravee.suthikulpanit@....com>
Subject: [PATCH v2 1/3] iommu: amd: Use 4K page for completion wait write-back semaphore

IOMMU SNP support requires the completion wait write-back semaphore to be
implemented using a 4K-aligned page, where the page address is to be
programmed into the newly introduced MMIO base/range registers.

This new scheme uses a per-iommu atomic variable to store the current
semaphore value, which is incremented for every completion wait command.

Since this new scheme is also compatible with non-SNP mode,
generalize the driver to use 4K page for completion-wait semaphore in
both modes.

Cc: Brijesh Singh <brijesh.singh@....com>
Signed-off-by: Suravee Suthikulpanit <suravee.suthikulpanit@....com>
---
 drivers/iommu/amd/amd_iommu_types.h |  3 ++-
 drivers/iommu/amd/init.c            | 18 ++++++++++++++++++
 drivers/iommu/amd/iommu.c           | 23 +++++++++++------------
 3 files changed, 31 insertions(+), 13 deletions(-)

diff --git a/drivers/iommu/amd/amd_iommu_types.h b/drivers/iommu/amd/amd_iommu_types.h
index 30a5d412255a..4c80483e78ec 100644
--- a/drivers/iommu/amd/amd_iommu_types.h
+++ b/drivers/iommu/amd/amd_iommu_types.h
@@ -595,7 +595,8 @@ struct amd_iommu {
 #endif
 
 	u32 flags;
-	volatile u64 __aligned(8) cmd_sem;
+	volatile u64 *cmd_sem;
+	u64 cmd_sem_val;
 
 #ifdef CONFIG_AMD_IOMMU_DEBUGFS
 	/* DebugFS Info */
diff --git a/drivers/iommu/amd/init.c b/drivers/iommu/amd/init.c
index 445a08d23fed..febc072f2717 100644
--- a/drivers/iommu/amd/init.c
+++ b/drivers/iommu/amd/init.c
@@ -813,6 +813,19 @@ static int iommu_init_ga(struct amd_iommu *iommu)
 	return ret;
 }
 
+static int __init alloc_cwwb_sem(struct amd_iommu *iommu)
+{
+	iommu->cmd_sem = (void *)get_zeroed_page(GFP_KERNEL);
+
+	return iommu->cmd_sem ? 0 : -ENOMEM;
+}
+
+static void __init free_cwwb_sem(struct amd_iommu *iommu)
+{
+	if (iommu->cmd_sem)
+		free_page((unsigned long)iommu->cmd_sem);
+}
+
 static void iommu_enable_xt(struct amd_iommu *iommu)
 {
 #ifdef CONFIG_IRQ_REMAP
@@ -1395,6 +1408,7 @@ static int __init init_iommu_from_acpi(struct amd_iommu *iommu,
 
 static void __init free_iommu_one(struct amd_iommu *iommu)
 {
+	free_cwwb_sem(iommu);
 	free_command_buffer(iommu);
 	free_event_buffer(iommu);
 	free_ppr_log(iommu);
@@ -1481,6 +1495,7 @@ static int __init init_iommu_one(struct amd_iommu *iommu, struct ivhd_header *h)
 	int ret;
 
 	raw_spin_lock_init(&iommu->lock);
+	iommu->cmd_sem_val = 0;
 
 	/* Add IOMMU to internal data structures */
 	list_add_tail(&iommu->list, &amd_iommu_list);
@@ -1558,6 +1573,9 @@ static int __init init_iommu_one(struct amd_iommu *iommu, struct ivhd_header *h)
 	if (!iommu->mmio_base)
 		return -ENOMEM;
 
+	if (alloc_cwwb_sem(iommu))
+		return -ENOMEM;
+
 	if (alloc_command_buffer(iommu))
 		return -ENOMEM;
 
diff --git a/drivers/iommu/amd/iommu.c b/drivers/iommu/amd/iommu.c
index 10e4200d3552..9e9898683537 100644
--- a/drivers/iommu/amd/iommu.c
+++ b/drivers/iommu/amd/iommu.c
@@ -792,11 +792,11 @@ irqreturn_t amd_iommu_int_handler(int irq, void *data)
  *
  ****************************************************************************/
 
-static int wait_on_sem(volatile u64 *sem)
+static int wait_on_sem(struct amd_iommu *iommu, u64 data)
 {
 	int i = 0;
 
-	while (*sem == 0 && i < LOOP_TIMEOUT) {
+	while (*iommu->cmd_sem != data && i < LOOP_TIMEOUT) {
 		udelay(1);
 		i += 1;
 	}
@@ -827,16 +827,16 @@ static void copy_cmd_to_buffer(struct amd_iommu *iommu,
 	writel(tail, iommu->mmio_base + MMIO_CMD_TAIL_OFFSET);
 }
 
-static void build_completion_wait(struct iommu_cmd *cmd, u64 address)
+static void build_completion_wait(struct iommu_cmd *cmd,
+				  struct amd_iommu *iommu,
+				  u64 data)
 {
-	u64 paddr = iommu_virt_to_phys((void *)address);
-
-	WARN_ON(address & 0x7ULL);
+	u64 paddr = iommu_virt_to_phys((void *)iommu->cmd_sem);
 
 	memset(cmd, 0, sizeof(*cmd));
 	cmd->data[0] = lower_32_bits(paddr) | CMD_COMPL_WAIT_STORE_MASK;
 	cmd->data[1] = upper_32_bits(paddr);
-	cmd->data[2] = 1;
+	cmd->data[2] = data;
 	CMD_SET_TYPE(cmd, CMD_COMPL_WAIT);
 }
 
@@ -1045,22 +1045,21 @@ static int iommu_completion_wait(struct amd_iommu *iommu)
 	struct iommu_cmd cmd;
 	unsigned long flags;
 	int ret;
+	u64 data;
 
 	if (!iommu->need_sync)
 		return 0;
 
-
-	build_completion_wait(&cmd, (u64)&iommu->cmd_sem);
-
 	raw_spin_lock_irqsave(&iommu->lock, flags);
 
-	iommu->cmd_sem = 0;
+	data = ++iommu->cmd_sem_val;
+	build_completion_wait(&cmd, iommu, data);
 
 	ret = __iommu_queue_command_sync(iommu, &cmd, false);
 	if (ret)
 		goto out_unlock;
 
-	ret = wait_on_sem(&iommu->cmd_sem);
+	ret = wait_on_sem(iommu, data);
 
 out_unlock:
 	raw_spin_unlock_irqrestore(&iommu->lock, flags);
-- 
2.17.1