diff mbox series

[2/5] x86/mm: Don't do a TLB flush if changing a PTE that isn't marked present

Message ID 1696011549-28036-3-git-send-email-mikelley@microsoft.com
State New
Headers
Series x86/coco: Mark CoCo VM pages not present when changing encrypted state |

Commit Message

Michael Kelley (LINUX) Sept. 29, 2023, 6:19 p.m. UTC 
  The core function __change_page_attr() currently sets up a TLB flush if
a PTE is changed. But if the old value of the PTE doesn't include the
PRESENT flag, the PTE won't be in the TLB, so a flush isn't needed.

Avoid an unnecessary TLB flush by conditioning the flush on the old
PTE value including PRESENT.  This change improves the performance of
functions like set_memory_p() by avoiding the flush if the memory range
was previously all not present.

Signed-off-by: Michael Kelley <mikelley@microsoft.com>
---
 arch/x86/mm/pat/set_memory.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)
diff mbox series

Patch

diff --git a/arch/x86/mm/pat/set_memory.c b/arch/x86/mm/pat/set_memory.c
index 8e19796..d7ef8d3 100644
--- a/arch/x86/mm/pat/set_memory.c
+++ b/arch/x86/mm/pat/set_memory.c
@@ -1636,7 +1636,10 @@  static int __change_page_attr(struct cpa_data *cpa, int primary)
 		 */
 		if (pte_val(old_pte) != pte_val(new_pte)) {
 			set_pte_atomic(kpte, new_pte);
-			cpa->flags |= CPA_FLUSHTLB;
+
+			/* If old_pte isn't present, it's not in the TLB */
+			if (pte_present(old_pte))
+				cpa->flags |= CPA_FLUSHTLB;
 		}
 		cpa->numpages = 1;
 		return 0;