Revert "iommu/amd: Skip enabling command/event buffers for kdump"

This reverts commit 44a764aec64b3f3235b9cbac2525222f69685418 which is
commit 9be15fb upstream.

This causes problems in older kernel trees as SNP host kdump is not
supported in them, so drop it from the stable branches.

Reported-by: Ashish Kalra <ashish.kalra@amd.com>
Link: https://lore.kernel.org/r/dacdff7f-0606-4ed5-b056-2de564404d51@amd.com
Cc: Vasant Hegde <vasant.hegde@amd.com>
Cc: Sairaj Kodilkar <sarunkod@amd.com>
Cc: Joerg Roedel <joerg.roedel@amd.com>
Cc: Sasha Levin <sashal@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
(cherry picked from commit bb4511b55fd37d77f4d2db4f8afcbd3e4c09b157)
Signed-off-by: Wentao Guan <guanwentao@uniontech.com>

Author: gregkh

drivers/iommu/amd/init.c

@@ -840,16 +840,11 @@ static void iommu_enable_command_buffer(struct amd_iommu *iommu)
 
 	BUG_ON(iommu->cmd_buf == NULL);
 
-	if (!is_kdump_kernel()) {
-		/*
-		 * Command buffer is re-used for kdump kernel and setting
-		 * of MMIO register is not required.
-		 */
-		entry = iommu_virt_to_phys(iommu->cmd_buf);
-		entry |= MMIO_CMD_SIZE_512;
-		memcpy_toio(iommu->mmio_base + MMIO_CMD_BUF_OFFSET,
-			    &entry, sizeof(entry));
-	}
+	entry = iommu_virt_to_phys(iommu->cmd_buf);
+	entry |= MMIO_CMD_SIZE_512;
+
+	memcpy_toio(iommu->mmio_base + MMIO_CMD_BUF_OFFSET,
+		    &entry, sizeof(entry));
 
 	amd_iommu_reset_cmd_buffer(iommu);
 }
@@ -898,15 +893,10 @@ static void iommu_enable_event_buffer(struct amd_iommu *iommu)
 
 	BUG_ON(iommu->evt_buf == NULL);
 
-	if (!is_kdump_kernel()) {
-		/*
-		 * Event buffer is re-used for kdump kernel and setting
-		 * of MMIO register is not required.
-		 */
-		entry = iommu_virt_to_phys(iommu->evt_buf) | EVT_LEN_MASK;
-		memcpy_toio(iommu->mmio_base + MMIO_EVT_BUF_OFFSET,
-			    &entry, sizeof(entry));
-	}
+	entry = iommu_virt_to_phys(iommu->evt_buf) | EVT_LEN_MASK;
+
+	memcpy_toio(iommu->mmio_base + MMIO_EVT_BUF_OFFSET,
+		    &entry, sizeof(entry));
 
 	/* set head and tail to zero manually */
 	writel(0x00, iommu->mmio_base + MMIO_EVT_HEAD_OFFSET);