From: Jan Beulich <jbeulich@suse.com>
Date: Tue, 29 Jun 2021 10:34:37 +0000 (+0200)
Subject: AMD/IOMMU: redo awaiting of command completion
X-Git-Tag: archive/raspbian/4.16.0+51-g0941d6cb-1+rpi1~2^2~42^2~378
X-Git-Url: https://dgit.raspbian.org/?a=commitdiff_plain;h=b175fc0c1274df34ff8bd89d603c88b014b22f10;p=xen.git

AMD/IOMMU: redo awaiting of command completion

The present abuse of the completion interrupt does not only stand in the
way of, down the road, using it for its actual purpose, but also
requires holding the IOMMU lock while waiting for command completion,
limiting parallelism and keeping interrupts off for non-negligible
periods of time. Have the IOMMU do an ordinary memory write instead of
signaling an otherwise disabled interrupt (by just updating a status
register bit).

Since IOMMU_COMP_WAIT_I_FLAG_SHIFT is now unused and
IOMMU_COMP_WAIT_[FS]_FLAG_SHIFT already were, drop all three of them
while at it.

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: Paul Durrant <paul@xen.org>
---

diff --git a/xen/drivers/passthrough/amd/iommu-defs.h b/xen/drivers/passthrough/amd/iommu-defs.h
index 0c97db2a32..774234dfd2 100644
--- a/xen/drivers/passthrough/amd/iommu-defs.h
+++ b/xen/drivers/passthrough/amd/iommu-defs.h
@@ -178,11 +178,8 @@ struct amd_iommu_dte {
 #define IOMMU_COMP_WAIT_DATA_BUFFER_SIZE	8
 #define IOMMU_COMP_WAIT_DATA_BUFFER_ALIGNMENT	8
 #define IOMMU_COMP_WAIT_S_FLAG_MASK		0x00000001
-#define IOMMU_COMP_WAIT_S_FLAG_SHIFT		0
 #define IOMMU_COMP_WAIT_I_FLAG_MASK		0x00000002
-#define IOMMU_COMP_WAIT_I_FLAG_SHIFT		1
 #define IOMMU_COMP_WAIT_F_FLAG_MASK		0x00000004
-#define IOMMU_COMP_WAIT_F_FLAG_SHIFT		2
 #define IOMMU_COMP_WAIT_ADDR_LOW_MASK		0xFFFFFFF8
 #define IOMMU_COMP_WAIT_ADDR_LOW_SHIFT		3
 #define IOMMU_COMP_WAIT_ADDR_HIGH_MASK		0x000FFFFF
diff --git a/xen/drivers/passthrough/amd/iommu_cmd.c b/xen/drivers/passthrough/amd/iommu_cmd.c
index 92a688dc9d..e8541276ca 100644
--- a/xen/drivers/passthrough/amd/iommu_cmd.c
+++ b/xen/drivers/passthrough/amd/iommu_cmd.c
@@ -20,6 +20,9 @@
 #include "iommu.h"
 #include "../ats.h"
 
+#define CMD_COMPLETION_INIT 0
+#define CMD_COMPLETION_DONE 1
+
 static void send_iommu_command(struct amd_iommu *iommu,
                                const uint32_t cmd[4])
 {
@@ -49,28 +52,27 @@ static void send_iommu_command(struct amd_iommu *iommu,
 static void flush_command_buffer(struct amd_iommu *iommu,
                                  unsigned int timeout_base)
 {
-    uint32_t cmd[4];
+    static DEFINE_PER_CPU(uint64_t, poll_slot);
+    uint64_t *this_poll_slot = &this_cpu(poll_slot);
+    paddr_t addr = virt_to_maddr(this_poll_slot);
+    /* send a COMPLETION_WAIT command to flush command buffer */
+    uint32_t cmd[4] = {
+        addr | MASK_INSR(IOMMU_CONTROL_ENABLED,
+                         IOMMU_COMP_WAIT_S_FLAG_MASK),
+        (addr >> 32) | MASK_INSR(IOMMU_CMD_COMPLETION_WAIT,
+                                 IOMMU_CMD_OPCODE_MASK),
+        CMD_COMPLETION_DONE
+    };
     s_time_t start, timeout;
     static unsigned int __read_mostly threshold = 1;
 
-    /* RW1C 'ComWaitInt' in status register */
-    writel(IOMMU_STATUS_COMP_WAIT_INT,
-           iommu->mmio_base + IOMMU_STATUS_MMIO_OFFSET);
+    ACCESS_ONCE(*this_poll_slot) = CMD_COMPLETION_INIT;
 
-    /* send an empty COMPLETION_WAIT command to flush command buffer */
-    cmd[3] = cmd[2] = 0;
-    set_field_in_reg_u32(IOMMU_CMD_COMPLETION_WAIT, 0,
-                         IOMMU_CMD_OPCODE_MASK,
-                         IOMMU_CMD_OPCODE_SHIFT, &cmd[1]);
-    set_field_in_reg_u32(IOMMU_CONTROL_ENABLED, 0,
-                         IOMMU_COMP_WAIT_I_FLAG_MASK,
-                         IOMMU_COMP_WAIT_I_FLAG_SHIFT, &cmd[0]);
     send_iommu_command(iommu, cmd);
 
     start = NOW();
     timeout = start + (timeout_base ?: 100) * MILLISECS(threshold);
-    while ( !(readl(iommu->mmio_base + IOMMU_STATUS_MMIO_OFFSET) &
-              IOMMU_STATUS_COMP_WAIT_INT) )
+    while ( ACCESS_ONCE(*this_poll_slot) != CMD_COMPLETION_DONE )
     {
         if ( timeout && NOW() > timeout )
         {