# \[PATCH v2 11/12\] x86/sev: Handle CLFLUSH MMIO events

- From: Joerg Roedel \<joro@8bytes.org\>
- Date: 2021-09-13 15:56:38 
- List: linux-coco
- Page: https://ratatoskr.run/linux-coco/2021/09/1506487
- Thread: https://ratatoskr.run/linux-coco/2021/09/1506481/t.md

```text
From: Joerg Roedel <redacted>

Handle CLFLUSH instruction to MMIO memory in the #VC handler. The
instruction is ignored by the handler, as the Hypervisor is
responsible for cache management of emulated MMIO memory.

Signed-off-by: Joerg Roedel <redacted>
---
 arch/x86/kernel/sev-shared.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/arch/x86/kernel/sev-shared.c b/arch/x86/kernel/sev-shared.c
index a7a0793c4f98..682fa202444f 100644
--- a/arch/x86/kernel/sev-shared.c
+++ b/arch/x86/kernel/sev-shared.c
@@ -632,6 +632,15 @@ static enum es_result vc_handle_mmio_twobyte_ops(struct ghcb *ghcb,
 	long *reg_data;
 
 	switch (insn->opcode.bytes[1]) {
+		/* CLFLUSH */
+	case 0xae:
+		/*
+		 * Ignore CLFLUSHes - those go to emulated MMIO anyway and the
+		 * hypervisor is responsible for cache management.
+		 */
+		ret = ES_OK;
+		break;
+
 		/* MMIO Read w/ zero-extension */
 	case 0xb6:
 		bytes = 1;
-- 
2.33.0

```