On Tue, Aug 04, 2026 at 01:31:04PM +0100, Pedro Falcato wrote: > On Tue, Aug 04, 2026 at 11:55:09AM +0100, Lorenzo Stoakes (ARM) wrote: > > 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. > > ACK. FTR, I think it would've been far clearer with "None of the contpte get > code". There is of course contpte code that needs write access (e.g > contpte_clear_full_ptes).
yeah that sounds better. Maybe just something like 'specify const for read-only users of pte *' or similar? > > > > > 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 :) > > *nods*. For what it's worth, this is new code that never needed extern. Yup, this isn't a big deal anyway :) > > > > > > 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 :( > > Me too! > > > > > Was it not possible to const-ify further to just be able to constify > > contpte_align_down itself? > > > > You can't do that because some callers want a pte_t* out of align_down, > others want a const pte_t* out of align_down, depending on the param. > > In A More Civilized Language(TM): > > template <typename T> > T contpte_align_down(T ptr); Now do it in rust ;) > > :P Well as per below you can just avoid the whole issue with: #define contpte_align_down(ptep) \ PTR_ALIGN_DOWN(ptep, sizeof(*(ptep)) * CONT_PTES) And avoid this mess? You're ultimately calling into a macro anyway. The generic thing Seems like a lot of hassle for an align-down, and then you're forcing a macro and nasty casts anyway so I don't really see the downside of just making it a macro in general? > > > 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. > > Yep, I'll admit the commit message is confusing and crap. I'll flesh it out > here. Thanks! > > > > > 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? > > Yep, seems like I mistakenly broke the coding style here and in the > contpte_align_down macro above (the \ is misaligned). I'll fix it up. > > (I think Andrew isn't taking more material for next cycle, and while > this should have no functional effect, it is very late and you have > pushback, so probably no rush here...) Yeah I assumed this was for 7.4 :) I mean the series is fine for 7.3 too AFAIC (with feedback addressed obviously). > > -- > Pedro -- Cheers, Lorenzo
