Messages in this thread | | | Date | Tue, 30 Apr 2024 12:11:12 +0100 | From | Catalin Marinas <> | Subject | Re: [PATCH v2 1/3] arm64/mm: Refactor PMD_PRESENT_INVALID and PTE_PROT_NONE bits |
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On Mon, Apr 29, 2024 at 06:15:45PM +0100, Ryan Roberts wrote: > On 29/04/2024 17:20, Catalin Marinas wrote: > > On Mon, Apr 29, 2024 at 03:02:05PM +0100, Ryan Roberts wrote: > >> diff --git a/arch/arm64/include/asm/pgtable-prot.h b/arch/arm64/include/asm/pgtable-prot.h > >> index dd9ee67d1d87..de62e6881154 100644 > >> --- a/arch/arm64/include/asm/pgtable-prot.h > >> +++ b/arch/arm64/include/asm/pgtable-prot.h > >> @@ -18,14 +18,7 @@ > >> #define PTE_DIRTY (_AT(pteval_t, 1) << 55) > >> #define PTE_SPECIAL (_AT(pteval_t, 1) << 56) > >> #define PTE_DEVMAP (_AT(pteval_t, 1) << 57) > >> -#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. > >> - */ > >> -#define PMD_PRESENT_INVALID (_AT(pteval_t, 1) << 59) /* only when !PMD_SECT_VALID */ > >> +#define PTE_INVALID (_AT(pteval_t, 1) << 59) /* only when !PTE_VALID */ > > > > Nitpick - I prefer the PTE_PRESENT_INVALID name as it makes it clearer > > it's a present pte. We already have PTE_VALID, calling it PTE_INVALID > > looks like a negation only. > > Meh, for me the pte can only be valid or invalid if it is present. So it's > implicit. And if you have PTE_PRESENT_INVALID you should also have > PTE_PRESENT_VALID. > > We also have pte_mkinvalid(), which is core-mm-defined. In your scheme, surely > it should be pte_mkpresent_invalid()? > > But you're the boss, I'll change this to PTE_PRESENT_INVALID. :-(
TBH, I don't have a strong opinion but best to avoid the bikeshedding. I'll leave the decision to you ;). It would match the pmd_mkinvalid() core code. But if you drop 'present' make sure you add a comment above that it's meant for present ptes.
> >> diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h > >> index afdd56d26ad7..8dd4637d6b56 100644 > >> --- a/arch/arm64/include/asm/pgtable.h > >> +++ b/arch/arm64/include/asm/pgtable.h > >> @@ -105,7 +105,7 @@ static inline pteval_t __phys_to_pte_val(phys_addr_t phys) > >> /* > >> * The following only work if pte_present(). Undefined behaviour otherwise. > >> */ > >> -#define pte_present(pte) (!!(pte_val(pte) & (PTE_VALID | PTE_PROT_NONE))) > >> +#define pte_present(pte) (pte_valid(pte) || pte_invalid(pte)) > >> #define pte_young(pte) (!!(pte_val(pte) & PTE_AF)) > >> #define pte_special(pte) (!!(pte_val(pte) & PTE_SPECIAL)) > >> #define pte_write(pte) (!!(pte_val(pte) & PTE_WRITE)) > >> @@ -132,6 +132,7 @@ static inline pteval_t __phys_to_pte_val(phys_addr_t phys) > >> #define pte_dirty(pte) (pte_sw_dirty(pte) || pte_hw_dirty(pte)) > >> > >> #define pte_valid(pte) (!!(pte_val(pte) & PTE_VALID)) > >> +#define pte_invalid(pte) ((pte_val(pte) & (PTE_VALID | PTE_INVALID)) == PTE_INVALID) [...] > > I think it's sufficient to check PTE_PRESENT_INVALID only. We'd never > > have both bits set, so no need for mask and compare. > > My rationale is that the INVALID bit may have some other HW meaning when > PTE_VALID is set, so its not correct to interpret it as INVALID unless VALID is > clear. Granted bit 59 is AttrIndex[3] or PBHA[0], neither of which we are using > currently so it will always be 0 when PTE_VALID=1 (and same argument when its > moved to NS in next patch). But it feels fragile to me. I'd rather leave it as > is unless you insist.
You are right. It currently works but it may overlap with some hardware bit on valid ptes.
> >> /* > >> * Execute-only user mappings do not have the PTE_USER bit set. All valid > >> * kernel mappings have the PTE_UXN bit set. > >> @@ -261,6 +262,13 @@ static inline pte_t pte_mkpresent(pte_t pte) > >> return set_pte_bit(pte, __pgprot(PTE_VALID)); > >> } > >> > >> +static inline pte_t pte_mkinvalid(pte_t pte) > >> +{ > >> + pte = set_pte_bit(pte, __pgprot(PTE_INVALID)); > >> + pte = clear_pte_bit(pte, __pgprot(PTE_VALID)); > >> + return pte; > >> +} > > > > I wonder whether we need to define this. I guess it makes sense than > > having the pmd_mkinvalid() use the PTE_* definitions directly, though it > > won't be something we need to do on a pte. > > For me its much cleaner to do it as is because it makes it clear that the format > is the same across pte, pmd and pud. And we need pte_invalid() (or > pte_present_invalid()) for PROT_NONE so isn't it better to match it with a setter?
I agree. It was just a remark above.
> >> static inline bool pmd_user_accessible_page(pmd_t pmd) > >> { > >> - return pmd_leaf(pmd) && !pmd_present_invalid(pmd) && (pmd_user(pmd) || pmd_user_exec(pmd)); > >> + return pmd_valid(pmd) && !pmd_table(pmd) && (pmd_user(pmd) || pmd_user_exec(pmd)); > >> } > > > > Maybe our pmd_leaf() should actually check valid && !table instead of > > present and no need to change these. > > I'm not sure that would be a great approach; pmd_leaf() is core-mm-defined. And > I can't imagine core-mm would want pmd_leaf() to start returning false after > calling pmd_mkinvalid(). You probably won't find anywhere where it actually > matters right now, but it would be subtly broken and could be exposed in future.
True, I think it's fine currently but you never know. So after pmd_mkinvalid() on a leaf pmd, pmd_leaf() should still return true. It might be worth adding a test to pmd_thp_tests() in debug_vm_pgtable.c.
> >> static inline bool pud_user_accessible_page(pud_t pud) > >> { > >> - return pud_leaf(pud) && (pud_user(pud) || pud_user_exec(pud)); > >> + return pud_valid(pud) && !pud_table(pud) && (pud_user(pud) || pud_user_exec(pud)); > >> } > >> #endif > > > > Same here. > > > > Otherwise I'm happy with the patch. Feel free to add: > > > > Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
My reviewed-by tag still stands even if you leave the patch as is.
Thanks.
-- Catalin
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