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X-OriginatorOrg: arm.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 02 Jun 2025 04:36:35.0236 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: 45142948-13b2-4a7f-2622-08dda18f0e73 X-MS-Exchange-CrossTenant-Id: f34e5979-57d9-4aaa-ad4d-b122a662184d X-MS-Exchange-CrossTenant-OriginalAttributedTenantConnectingIp: TenantId=f34e5979-57d9-4aaa-ad4d-b122a662184d;Ip=[4.158.2.129];Helo=[outbound-uk1.az.dlp.m.darktrace.com] X-MS-Exchange-CrossTenant-AuthSource: DB1PEPF000509E7.eurprd03.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: DBBPR08MB6234 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20250601_213644_770054_C1D3B80E X-CRM114-Status: GOOD ( 17.89 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On 30/05/25 6:23 pm, Ryan Roberts wrote: > On 30/05/2025 10:04, Dev Jain wrote: >> Move away from apply_to_page_range(), which does not honour leaf mappings, >> to walk_page_range_novma(). The callbacks emit a warning and return EINVAL >> if a partial range is detected. > Perhaps: > > """ > apply_to_page_range(), which was previously used to change permissions for > kernel mapped memory, can only operate on page mappings. In future we want to > support block mappings for more efficient TLB usage. Reimplement pageattr.c to > instead use walk_page_range_novma() to visit and modify leaf mappings of all sizes. > > We only require that the start and end of a given range lie on leaf mapping > boundaries. If this is not the case, emit a warning and return -EINVAL. > """ Thanks. > >> Signed-off-by: Dev Jain >> --- >> arch/arm64/mm/pageattr.c | 69 +++++++++++++++++++++++++++++++++++++--- >> 1 file changed, 64 insertions(+), 5 deletions(-) >> >> diff --git a/arch/arm64/mm/pageattr.c b/arch/arm64/mm/pageattr.c >> index 39fd1f7ff02a..a5c829c64969 100644 >> --- a/arch/arm64/mm/pageattr.c >> +++ b/arch/arm64/mm/pageattr.c >> @@ -8,6 +8,7 @@ >> #include >> #include >> #include >> +#include >> >> #include >> #include >> @@ -20,6 +21,67 @@ struct page_change_data { >> pgprot_t clear_mask; >> }; >> >> +static pteval_t set_pageattr_masks(unsigned long val, struct mm_walk *walk) > Please don't use unsigned long for raw ptes; This will break with D128 pgtables. > > Anshuman had a patch in flight to introduce ptdesc_t as a generic/any level raw > value. It would be preferable to incorporate that patch and use it. pteval_t > isn't really correct because this is for any level and that implies pte level only. Okay. > >> +{ >> + struct page_change_data *masks = walk->private; >> + unsigned long new_val = val; > why do you need new_val? Why not just update and return val? Yes, shameless copying from riscv and loongarch : ) > >> + >> + new_val &= ~(pgprot_val(masks->clear_mask)); >> + new_val |= (pgprot_val(masks->set_mask)); >> + >> + return new_val; >> +} > One potential pitfall of having a generic function that can change the > permissions for ptes at all levels is that bit 1 is defined differently for > level 3 vs the other levels. I don't think there should be any issues here in > practice having had a quick look at all the masks that users currently pass in > though. > >> + >> +static int pageattr_pud_entry(pud_t *pud, unsigned long addr, >> + unsigned long next, struct mm_walk *walk) >> +{ >> + pud_t val = pudp_get(pud); >> + >> + if (pud_leaf(val)) { >> + if (WARN_ON_ONCE((next - addr) != PUD_SIZE)) >> + return -EINVAL; >> + val = __pud(set_pageattr_masks(pud_val(val), walk)); >> + set_pud(pud, val); >> + walk->action = ACTION_CONTINUE; >> + } >> + >> + return 0; >> +} >> + >> +static int pageattr_pmd_entry(pmd_t *pmd, unsigned long addr, >> + unsigned long next, struct mm_walk *walk) >> +{ >> + pmd_t val = pmdp_get(pmd); >> + >> + if (pmd_leaf(val)) { >> + if (WARN_ON_ONCE((next - addr) != PMD_SIZE)) >> + return -EINVAL; >> + val = __pmd(set_pageattr_masks(pmd_val(val), walk)); >> + set_pmd(pmd, val); >> + walk->action = ACTION_CONTINUE; >> + } >> + >> + return 0; >> +} >> + >> +static int pageattr_pte_entry(pte_t *pte, unsigned long addr, >> + unsigned long next, struct mm_walk *walk) >> +{ >> + pte_t val = ptep_get(pte); > BUG: Use __ptep_get(), which is "below" the contpte management layer. ptep_get() > will look at the contiguous bit and potentially decide to accumulate all the a/d > bits in the block which is not relavent for kernel mappings. Thanks. > >> + >> + val = __pte(set_pageattr_masks(pte_val(val), walk)); >> + set_pte(pte, val); > BUG: Use __set_pte(). Same reasoning as above. But this is more harmful because > set_pte() will try to detect contpte blocks and may zero/flush the entries. > Which would be very bad for kernel mappings. Thanks. > >> + >> + return 0; >> +} >> + >> +static const struct mm_walk_ops pageattr_ops = { >> + .pud_entry = pageattr_pud_entry, >> + .pmd_entry = pageattr_pmd_entry, >> + .pte_entry = pageattr_pte_entry, > Is there a reason why you don't have pgd and p4d entries? I think there are > configs where the pgd may contain leaf mappings. Possibly 64K/42-bit, which will > have 2 levels and I think they will be pgd and pte. So I think you'd better > implement all levels to be correct. Okay. > >> + .walk_lock = PGWALK_NOLOCK, >> +}; >> + >> bool rodata_full __ro_after_init = IS_ENABLED(CONFIG_RODATA_FULL_DEFAULT_ENABLED); >> >> bool can_set_direct_map(void) >> @@ -49,9 +111,6 @@ static int change_page_range(pte_t *ptep, unsigned long addr, void *data) >> return 0; >> } >> >> -/* >> - * This function assumes that the range is mapped with PAGE_SIZE pages. >> - */ >> static int __change_memory_common(unsigned long start, unsigned long size, >> pgprot_t set_mask, pgprot_t clear_mask) >> { >> @@ -61,8 +120,8 @@ static int __change_memory_common(unsigned long start, unsigned long size, >> data.set_mask = set_mask; >> data.clear_mask = clear_mask; >> >> - ret = apply_to_page_range(&init_mm, start, size, change_page_range, >> - &data); >> + ret = walk_page_range_novma(&init_mm, start, start + size, >> + &pageattr_ops, NULL, &data); >> >> /* >> * If the memory is being made valid without changing any other bits > I notice that set_direct_map_invalid_noflush() and > set_direct_map_default_noflush() don't use __change_memory_common() but instead > call apply_to_page_range() direct. (presumably because they don't want the > associated tlb flush). Is there a reason not to update these callers too? > > Perhaps it would be cleaner to wrap in ___change_memory_common (3 leading > underscores) which does everything except the flush). Makes sense, I think Yang's series will need this to handle block mappings for linear map. > > Thanks, > Ryan >