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Message-ID: <20240503144604.151095-3-ryan.roberts@arm.com>
Date: Fri, 3 May 2024 15:46:00 +0100
From: Ryan Roberts <ryan.roberts@....com>
To: Catalin Marinas <catalin.marinas@....com>,
Will Deacon <will@...nel.org>,
Joey Gouly <joey.gouly@....com>,
Ard Biesheuvel <ardb@...nel.org>,
Mark Rutland <mark.rutland@....com>,
Anshuman Khandual <anshuman.khandual@....com>,
David Hildenbrand <david@...hat.com>,
Peter Xu <peterx@...hat.com>,
Mike Rapoport <rppt@...ux.ibm.com>,
Shivansh Vij <shivanshvij@...look.com>
Cc: Ryan Roberts <ryan.roberts@....com>,
linux-arm-kernel@...ts.infradead.org,
linux-kernel@...r.kernel.org
Subject: [PATCH v4 2/4] arm64/mm: Remove PTE_PROT_NONE bit
Currently the PTE_PRESENT_INVALID and PTE_PROT_NONE functionality
explicitly occupy 2 bits in the PTE when PTE_VALID/PMD_SECT_VALID is
clear. This has 2 significant consequences:
- PTE_PROT_NONE consumes a precious SW PTE bit that could be used for
other things.
- The swap pte layout must reserve those same 2 bits and ensure they
are both always zero for a swap pte. It would be nice to reclaim at
least one of those bits.
But PTE_PRESENT_INVALID, which since the previous patch, applies
uniformly to page/block descriptors at any level when PTE_VALID is
clear, can already give us most of what PTE_PROT_NONE requires: If it is
set, then the pte is still considered present; pte_present() returns
true and all the fields in the pte follow the HW interpretation (e.g. SW
can safely call pte_pfn(), etc). But crucially, the HW treats the pte as
invalid and will fault if it hits.
So let's remove PTE_PROT_NONE entirely and instead represent PROT_NONE
as a present but invalid pte (PTE_VALID=0, PTE_PRESENT_INVALID=1) with
PTE_USER=0 and PTE_UXN=1. This is a unique combination that is not used
anywhere else.
The net result is a clearer, simpler, more generic encoding scheme that
applies uniformly to all levels. Additionally we free up a PTE SW bit
and a swap pte bit (bit 58 in both cases).
Reviewed-by: Catalin Marinas <catalin.marinas@....com>
Signed-off-by: Ryan Roberts <ryan.roberts@....com>
---
arch/arm64/include/asm/pgtable-prot.h | 3 +--
arch/arm64/include/asm/pgtable.h | 31 +++++++++++++++------------
2 files changed, 18 insertions(+), 16 deletions(-)
diff --git a/arch/arm64/include/asm/pgtable-prot.h b/arch/arm64/include/asm/pgtable-prot.h
index cdbf51eef7a6..81f07b44f7b8 100644
--- a/arch/arm64/include/asm/pgtable-prot.h
+++ b/arch/arm64/include/asm/pgtable-prot.h
@@ -18,7 +18,6 @@
#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 */
/*
* PTE_PRESENT_INVALID=1 & PTE_VALID=0 indicates that the pte's fields should be
@@ -103,7 +102,7 @@ static inline bool __pure lpa2_is_enabled(void)
__val; \
})
-#define PAGE_NONE __pgprot(((_PAGE_DEFAULT) & ~PTE_VALID) | PTE_PROT_NONE | PTE_RDONLY | PTE_NG | PTE_PXN | PTE_UXN)
+#define PAGE_NONE __pgprot(((_PAGE_DEFAULT) & ~PTE_VALID) | PTE_PRESENT_INVALID | PTE_RDONLY | PTE_NG | PTE_PXN | PTE_UXN)
/* shared+writable pages are clean by default, hence PTE_RDONLY|PTE_WRITE */
#define PAGE_SHARED __pgprot(_PAGE_SHARED)
#define PAGE_SHARED_EXEC __pgprot(_PAGE_SHARED_EXEC)
diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h
index 7156c940ac4f..c0f4471423db 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_present_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))
@@ -478,7 +478,16 @@ static inline pte_t pte_swp_clear_exclusive(pte_t pte)
*/
static inline int pte_protnone(pte_t pte)
{
- return (pte_val(pte) & (PTE_VALID | PTE_PROT_NONE)) == PTE_PROT_NONE;
+ /*
+ * pte_present_invalid() tells us that the pte is invalid from HW
+ * perspective but present from SW perspective, so the fields are to be
+ * interpretted as per the HW layout. The second 2 checks are the unique
+ * encoding that we use for PROT_NONE. It is insufficient to only use
+ * the first check because we share the same encoding scheme with pmds
+ * which support pmd_mkinvalid(), so can be present-invalid without
+ * being PROT_NONE.
+ */
+ return pte_present_invalid(pte) && !pte_user(pte) && !pte_user_exec(pte);
}
static inline int pmd_protnone(pmd_t pmd)
@@ -487,12 +496,7 @@ static inline int pmd_protnone(pmd_t pmd)
}
#endif
-#define pmd_present_invalid(pmd) pte_present_invalid(pmd_pte(pmd))
-
-static inline int pmd_present(pmd_t pmd)
-{
- return pte_present(pmd_pte(pmd)) || pmd_present_invalid(pmd);
-}
+#define pmd_present(pmd) pte_present(pmd_pte(pmd))
/*
* THP definitions.
@@ -1029,8 +1033,8 @@ static inline pte_t pte_modify(pte_t pte, pgprot_t newprot)
* in MAIR_EL1. The mask below has to include PTE_ATTRINDX_MASK.
*/
const pteval_t mask = PTE_USER | PTE_PXN | PTE_UXN | PTE_RDONLY |
- PTE_PROT_NONE | PTE_VALID | PTE_WRITE | PTE_GP |
- PTE_ATTRINDX_MASK;
+ PTE_PRESENT_INVALID | PTE_VALID | PTE_WRITE |
+ PTE_GP | PTE_ATTRINDX_MASK;
/* preserve the hardware dirty information */
if (pte_hw_dirty(pte))
pte = set_pte_bit(pte, __pgprot(PTE_DIRTY));
@@ -1078,17 +1082,17 @@ static inline int pgd_devmap(pgd_t pgd)
#ifdef CONFIG_PAGE_TABLE_CHECK
static inline bool pte_user_accessible_page(pte_t pte)
{
- return pte_present(pte) && (pte_user(pte) || pte_user_exec(pte));
+ return pte_valid(pte) && (pte_user(pte) || pte_user_exec(pte));
}
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));
}
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
@@ -1252,7 +1256,6 @@ static inline pmd_t pmdp_establish(struct vm_area_struct *vma,
* bits 2: remember PG_anon_exclusive
* bits 3-7: swap type
* bits 8-57: swap offset
- * bit 58: PTE_PROT_NONE (must be zero)
* bit 59: PTE_PRESENT_INVALID (must be zero)
*/
#define __SWP_TYPE_SHIFT 3
--
2.43.0
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