[PATCH v2] iommu/amd: Do not clear event/ppr log buffer when snp is enabled

[PATCH v2] iommu/amd: Do not clear event/ppr log buffer when snp is enabled

[Vasant Hegde]

From: Tom Lendacky <thomas.lendacky@amd.com>

Current code clears event log and ppr log entry after processing it due
to hardware errata ([1]  erratum #732, #733). We do not have hardware
issue on SNP enabled system.

When SNP is enabled, the event logs, PPR log and completion wait buffer
are read-only to the host (see SNP FW ABI spec [2]). Clearing those entry
will result in a kernel #PF for an RMP violation. Hence do not clear
event and ppr log entry after processing it.

[1] http://developer.amd.com/wordpress/media/2012/10/48931_15h_Mod_10h-1Fh_Rev_Guide.pdf
[2] https://www.amd.com/system/files/TechDocs/56860.pdf

Signed-off-by: Tom Lendacky <thomas.lendacky@amd.com>
Signed-off-by: Vasant Hegde <vasant.hegde@amd.com>
Reviewed-by: Suravee Suthikulpanit <suravee.suthikulpanit@amd.com>
---
Changes in v2:
  - As suggested by Joerg, expanded comment to cover SNP enabled system.

-Vasant

 drivers/iommu/amd/iommu.c | 18 ++++++++++++++----
 1 file changed, 14 insertions(+), 4 deletions(-)

diff --git a/drivers/iommu/amd/iommu.c b/drivers/iommu/amd/iommu.c
index cbeaab55c0db..367e583ef29e 100644
--- a/drivers/iommu/amd/iommu.c
+++ b/drivers/iommu/amd/iommu.c
@@ -667,7 +667,14 @@ static void iommu_print_event(struct amd_iommu *iommu, void *__evt)
 			event[0], event[1], event[2], event[3]);
 	}
 
-	memset(__evt, 0, 4 * sizeof(u32));
+	/*
+	 * To detect the hardware errata 732 we need to clear the
+	 * entry back to zero. This issue does not exist on SNP
+	 * enabled system. Also this buffer is not writeable on
+	 * SNP enabled system.
+	 */
+	if (!amd_iommu_snp_en)
+		memset(__evt, 0, 4 * sizeof(u32));
 }
 
 static void iommu_poll_events(struct amd_iommu *iommu)
@@ -736,10 +743,13 @@ static void iommu_poll_ppr_log(struct amd_iommu *iommu)
 		entry[1] = raw[1];
 
 		/*
-		 * To detect the hardware bug we need to clear the entry
-		 * back to zero.
+		 * To detect the hardware errata 733 we need to clear the
+		 * entry back to zero. This issue does not exist on SNP
+		 * enabled system. Also this buffer is not writeable on
+		 * SNP enabled system.
 		 */
-		raw[0] = raw[1] = 0UL;
+		if (!amd_iommu_snp_en)
+			raw[0] = raw[1] = 0UL;
 
 		/* Update head pointer of hardware ring-buffer */
 		head = (head + PPR_ENTRY_SIZE) % PPR_LOG_SIZE;
-- 
2.31.1

Re: [PATCH v2] iommu/amd: Do not clear event/ppr log buffer when snp is enabled

[Joerg Roedel]

On Tue, Jan 17, 2023 at 04:40:38AM +0000, Vasant Hegde wrote:
>  drivers/iommu/amd/iommu.c | 18 ++++++++++++++----
>  1 file changed, 14 insertions(+), 4 deletions(-)

Applied, thanks Vasant and Tom.