| Message ID | 20240327143858.711792-3-samuel.holland@sifive.com (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | riscv: access_ok() optimization | expand |
On Wed, Mar 27, 2024, at 15:38, Samuel Holland wrote: > TASK_SIZE_MAX should be set to a constant value, at least the largest > valid userspace address under any runtime configuration. This optimizes > the check in __access_ok(), which no longer needs to compute the runtime > value of TASK_SIZE. The check does not need to be exact, as long as it > accepts all valid userspace addresses and rejects all valid kernel > addresses; well-behaved programs will never fail the access_ok() check. > > For RISC-V, which requires all virtual addresses to be sign extended, > the optimal choice is LONG_MAX because it simplifies the limit > comparison to a sign bit test. > > This removes about half of the references to pgtable_l[45]_enabled. > > Signed-off-by: Samuel Holland <samuel.holland@sifive.com> Reviewed-by: Arnd Bergmann <arnd@arndb.de>
On 27/03/2024 15:38, Samuel Holland wrote: > TASK_SIZE_MAX should be set to a constant value, at least the largest > valid userspace address under any runtime configuration. This optimizes > the check in __access_ok(), which no longer needs to compute the runtime > value of TASK_SIZE. The check does not need to be exact, as long as it > accepts all valid userspace addresses and rejects all valid kernel > addresses; well-behaved programs will never fail the access_ok() check. > > For RISC-V, which requires all virtual addresses to be sign extended, > the optimal choice is LONG_MAX because it simplifies the limit > comparison to a sign bit test. > > This removes about half of the references to pgtable_l[45]_enabled. > > Signed-off-by: Samuel Holland <samuel.holland@sifive.com> > --- > > Changes in v2: > - Set TASK_SIZE_MAX to LONG_MAX to optimize the comparison > - Reword the commit message > > arch/riscv/include/asm/pgtable.h | 1 + > 1 file changed, 1 insertion(+) > > diff --git a/arch/riscv/include/asm/pgtable.h b/arch/riscv/include/asm/pgtable.h > index f5cc8bcc7f8d..762a85551764 100644 > --- a/arch/riscv/include/asm/pgtable.h > +++ b/arch/riscv/include/asm/pgtable.h > @@ -870,6 +870,7 @@ static inline pte_t pte_swp_clear_exclusive(pte_t pte) > */ > #ifdef CONFIG_64BIT > #define TASK_SIZE_64 (PGDIR_SIZE * PTRS_PER_PGD / 2) > +#define TASK_SIZE_MAX LONG_MAX > > #ifdef CONFIG_COMPAT > #define TASK_SIZE_32 (_AC(0x80000000, UL) - PAGE_SIZE) You can add: Reviewed-by: Alexandre Ghiti <alexghiti@rivosinc.com> Thanks, Alex
diff --git a/arch/riscv/include/asm/pgtable.h b/arch/riscv/include/asm/pgtable.h index f5cc8bcc7f8d..762a85551764 100644 --- a/arch/riscv/include/asm/pgtable.h +++ b/arch/riscv/include/asm/pgtable.h @@ -870,6 +870,7 @@ static inline pte_t pte_swp_clear_exclusive(pte_t pte) */ #ifdef CONFIG_64BIT #define TASK_SIZE_64 (PGDIR_SIZE * PTRS_PER_PGD / 2) +#define TASK_SIZE_MAX LONG_MAX #ifdef CONFIG_COMPAT #define TASK_SIZE_32 (_AC(0x80000000, UL) - PAGE_SIZE)
TASK_SIZE_MAX should be set to a constant value, at least the largest valid userspace address under any runtime configuration. This optimizes the check in __access_ok(), which no longer needs to compute the runtime value of TASK_SIZE. The check does not need to be exact, as long as it accepts all valid userspace addresses and rejects all valid kernel addresses; well-behaved programs will never fail the access_ok() check. For RISC-V, which requires all virtual addresses to be sign extended, the optimal choice is LONG_MAX because it simplifies the limit comparison to a sign bit test. This removes about half of the references to pgtable_l[45]_enabled. Signed-off-by: Samuel Holland <samuel.holland@sifive.com> --- Changes in v2: - Set TASK_SIZE_MAX to LONG_MAX to optimize the comparison - Reword the commit message arch/riscv/include/asm/pgtable.h | 1 + 1 file changed, 1 insertion(+)