On Tue, Feb 20, 2024 at 06:25:43PM +0800, Baoquan He wrote:
> > I am not sure what part of the comment you see doesn't reflect the
> > behaviour. From my PoV, changed code matches the comment closer that
> > original.
>
> Oh, I didn't make it clear. I mean update the code comment for
> lookup_address(), and add code comment for lookup_address_in_pgd() to
> mention the level thing. Maybe it's a chance to do that.
>
> ===1>
> *
> * Lookup the page table entry for a virtual address. Return a pointer
> * to the entry and the level of the mapping.
> *
> * Note: We return pud and pmd either when the entry is marked large
> ~~~~~~~~~~~ seems we return p4d too
> * or when the present bit is not set. Otherwise we would return a
> * pointer to a nonexisting mapping.
> ~~~~~~~~~~~~~~~ NULL?
> */
> pte_t *lookup_address(unsigned long address, unsigned int *level)
> {
> return lookup_address_in_pgd(pgd_offset_k(address), address, level);
> }
> EXPORT_SYMBOL_GPL(lookup_address);
> ===
>
> ===2>
> /*
> * Lookup the page table entry for a virtual address in a specific pgd.
> * Return a pointer to the entry and the level of the mapping.
> ~~ also could return NULL if it's none entry. And do we need to
> mention the level thing?
> */
> pte_t *lookup_address_in_pgd(pgd_t *pgd, unsigned long address,
> unsigned int *level)
> ...
> }
>
What about this fixup:
diff --git a/arch/x86/mm/pat/set_memory.c b/arch/x86/mm/pat/set_memory.c
index 3612e3167147..425ff6e192e6 100644
--- a/arch/x86/mm/pat/set_memory.c
+++ b/arch/x86/mm/pat/set_memory.c
@@ -657,7 +657,8 @@ static inline pgprot_t verify_rwx(pgprot_t old, pgprot_t new, unsigned long star
/*
* Lookup the page table entry for a virtual address in a specific pgd.
- * Return a pointer to the entry and the level of the mapping.
+ * Return a pointer to the entry and the level of the mapping (or NULL if
+ * the entry is none) and level of the entry.
*/
pte_t *lookup_address_in_pgd(pgd_t *pgd, unsigned long address,
unsigned int *level)
@@ -704,9 +705,8 @@ pte_t *lookup_address_in_pgd(pgd_t *pgd, unsigned long address,
* Lookup the page table entry for a virtual address. Return a pointer
* to the entry and the level of the mapping.
*
- * Note: We return pud and pmd either when the entry is marked large
- * or when the present bit is not set. Otherwise we would return a
- * pointer to a nonexisting mapping.
+ * Note: the function returns p4d, pud and pmd either when the entry is marked
+ * large or when the present bit is not set. Otherwise it returns NULL.
*/
pte_t *lookup_address(unsigned long address, unsigned int *level)
{
--
Kiryl Shutsemau / Kirill A. Shutemov
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