Re: [PATCH v4 1/4] arm64/mm: generalize PMD_PRESENT_INVALID for all levels

From: David Hildenbrand
Date: Tue May 07 2024 - 07:39:00 EST


On 03.05.24 16:45, Ryan Roberts wrote:
As preparation for the next patch, which frees up the PTE_PROT_NONE
present pte and swap pte bit, generalize PMD_PRESENT_INVALID to
PTE_PRESENT_INVALID. This will then be used to mark PROT_NONE ptes (and
entries at any other level) in the next patch.

While we're at it, fix up the swap pte format comment to include
PTE_PRESENT_INVALID. This is not new, it just wasn't previously
documented.

Reviewed-by: Catalin Marinas <catalin.marinas@xxxxxxx>
Signed-off-by: Ryan Roberts <ryan.roberts@xxxxxxx>
---
arch/arm64/include/asm/pgtable-prot.h | 8 ++++----
arch/arm64/include/asm/pgtable.h | 21 ++++++++++++---------
2 files changed, 16 insertions(+), 13 deletions(-)

diff --git a/arch/arm64/include/asm/pgtable-prot.h b/arch/arm64/include/asm/pgtable-prot.h
index dd9ee67d1d87..cdbf51eef7a6 100644
--- a/arch/arm64/include/asm/pgtable-prot.h
+++ b/arch/arm64/include/asm/pgtable-prot.h
@@ -21,11 +21,11 @@
#define PTE_PROT_NONE (_AT(pteval_t, 1) << 58) /* only when !PTE_VALID */
/*
- * This bit indicates that the entry is present i.e. pmd_page()
- * still points to a valid huge page in memory even if the pmd
- * has been invalidated.
+ * PTE_PRESENT_INVALID=1 & PTE_VALID=0 indicates that the pte's fields should be
+ * interpreted according to the HW layout by SW but any attempted HW access to
+ * the address will result in a fault. pte_present() returns true.
*/
-#define PMD_PRESENT_INVALID (_AT(pteval_t, 1) << 59) /* only when !PMD_SECT_VALID */
+#define PTE_PRESENT_INVALID (_AT(pteval_t, 1) << 59) /* only when !PTE_VALID */

Ah, so PTE_VALID == PMD_SECT_VALID. Would that also be a reasonable generalization independent of this? (or do we keep it as is because it's a HW def?)

Reviewed-by: David Hildenbrand <david@xxxxxxxxxx>


--
Cheers,

David / dhildenb