On Mon, Aug 03, 2026 at 05:43:55PM +0100, Pedro Falcato wrote: > None of the contpte code needs write access to the PTEs.
This seems like a very broad statement? Is that actually true? I see a bunch of ptep's that aren't const-ified, so you should explain why those couldn't be converted. Also you add a new contpte_align_down() macro, you should mention that it the commit message, explain why it was needed. In general more needed here :) it'd be ok if it was a truly trivial change that was all obvious but you're changing some pte_t *'s and not others so it's clearly not. > > Signed-off-by: Pedro Falcato <[email protected]> > --- > arch/arm64/include/asm/pgtable.h | 10 +++++----- > arch/arm64/mm/contpte.c | 11 ++++++++--- > 2 files changed, 13 insertions(+), 8 deletions(-) > > diff --git a/arch/arm64/include/asm/pgtable.h > b/arch/arm64/include/asm/pgtable.h > index a2681d755358..043bc0649cee 100644 > --- a/arch/arm64/include/asm/pgtable.h > +++ b/arch/arm64/include/asm/pgtable.h > @@ -378,7 +378,7 @@ static inline void __set_pte(pte_t *ptep, pte_t pte) > __set_pte_complete(pte); > } > > -static inline pte_t __ptep_get(pte_t *ptep) > +static inline pte_t __ptep_get(const pte_t *ptep) > { > return READ_ONCE(*ptep); > } > @@ -1652,8 +1652,8 @@ extern void __contpte_try_fold(struct mm_struct *mm, > unsigned long addr, > pte_t *ptep, pte_t pte); > extern void __contpte_try_unfold(struct mm_struct *mm, unsigned long addr, > pte_t *ptep, pte_t pte); > -extern pte_t contpte_ptep_get(pte_t *ptep, pte_t orig_pte); > -extern pte_t contpte_ptep_get_lockless(pte_t *orig_ptep); > +extern pte_t contpte_ptep_get(const pte_t *ptep, pte_t orig_pte); > +extern pte_t contpte_ptep_get_lockless(const pte_t *orig_ptep); This is (very) nitty but - not sure on the policy on extern's (Will/Catalin?) - but in mm we drop them when we touch the code since you don't need them these days :) > extern void contpte_set_ptes(struct mm_struct *mm, unsigned long addr, > pte_t *ptep, pte_t pte, unsigned int nr); > extern void contpte_clear_full_ptes(struct mm_struct *mm, unsigned long addr, > @@ -1732,7 +1732,7 @@ static inline unsigned int pte_batch_hint(pte_t *ptep, > pte_t pte) > */ > > #define ptep_get ptep_get > -static inline pte_t ptep_get(pte_t *ptep) > +static inline pte_t ptep_get(const pte_t *ptep) > { > pte_t pte = __ptep_get(ptep); > > @@ -1743,7 +1743,7 @@ static inline pte_t ptep_get(pte_t *ptep) > } > > #define ptep_get_lockless ptep_get_lockless > -static inline pte_t ptep_get_lockless(pte_t *ptep) > +static inline pte_t ptep_get_lockless(const pte_t *ptep) > { > pte_t pte = __ptep_get(ptep); > > diff --git a/arch/arm64/mm/contpte.c b/arch/arm64/mm/contpte.c > index 2de12656b4d8..3a5d6937fb51 100644 > --- a/arch/arm64/mm/contpte.c > +++ b/arch/arm64/mm/contpte.c > @@ -26,6 +26,11 @@ static inline pte_t *contpte_align_down(pte_t *ptep) > return PTR_ALIGN_DOWN(ptep, sizeof(*ptep) * CONT_PTES); > } > > +#define contpte_align_down(ptep) > \ > + _Generic((ptep), > \ > + const pte_t *: (const pte_t *) contpte_align_down((pte_t *) > (ptep)), \ > + pte_t *: contpte_align_down((pte_t *) ptep)) I really hate these _Generic() helper things. So ugly. And it's a pretty horrid cast now :( Was it not possible to const-ify further to just be able to constify contpte_align_down itself? It also seems to contradict the claim that contpte doesn't need write-access to pte's since you're going to lengths to allow non-const pte_t * here. You should cover off why this was necessary in the commit message as above. Anyway PTR_ALIGN_DOWN() is already const-safe so couldn't you anyway just collapse this to: #define contpte_align_down(ptep) \ PTR_ALIGN_DOWN(ptep, sizeof(*(ptep)) * CONT_PTES) Then describe in the commit message why you need to handle both cases? > + > static inline pte_t *contpte_align_addr_ptep(unsigned long *start, > unsigned long *end, pte_t *ptep, > unsigned int nr) > @@ -310,7 +315,7 @@ void __contpte_try_unfold(struct mm_struct *mm, unsigned > long addr, > } > EXPORT_SYMBOL_GPL(__contpte_try_unfold); > > -pte_t contpte_ptep_get(pte_t *ptep, pte_t orig_pte) > +pte_t contpte_ptep_get(const pte_t *ptep, pte_t orig_pte) > { > /* > * Gather access/dirty bits, which may be populated in any of the ptes > @@ -367,7 +372,7 @@ static inline bool contpte_is_consistent(pte_t pte, > unsigned long pfn, > pgprot_val(prot) == pgprot_val(orig_prot); > } > > -pte_t contpte_ptep_get_lockless(pte_t *orig_ptep) > +pte_t contpte_ptep_get_lockless(const pte_t *orig_ptep) > { > /* > * The ptep_get_lockless() API requires us to read and return *orig_ptep > @@ -386,10 +391,10 @@ pte_t contpte_ptep_get_lockless(pte_t *orig_ptep) > * because it is not part of a contpte range. > */ > > + const pte_t *ptep; Nit but this is breaking the reverse xmas tree isn't it? > pgprot_t orig_prot; > unsigned long pfn; > pte_t orig_pte; > - pte_t *ptep; > pte_t pte; > int i; > > -- > 2.55.0 > -- Cheers, Lorenzo
