Messages in this thread Patch in this message | | | From | Leonardo Bras <> | Subject | Re: [PATCH V2 1/4] riscv: mm: Fixup compat mode boot failure | Date | Thu, 21 Dec 2023 22:51:04 -0300 |
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Hello Guo Ren,
On Thu, Dec 21, 2023 at 10:46:58AM -0500, guoren@kernel.org wrote: > From: Guo Ren <guoren@linux.alibaba.com> > > In COMPAT mode, the STACK_TOP is 0x80000000, but the TASK_SIZE is > 0x7fff000. When the user stack is upon 0x7fff000, it will cause a user > segment fault. Sometimes, it would cause boot failure when the whole > rootfs is rv32.
Checking if I get the scenario:
In pgtable.h: #ifdef CONFIG_64BIT #define TASK_SIZE_64 (PGDIR_SIZE * PTRS_PER_PGD / 2) #define TASK_SIZE_MIN (PGDIR_SIZE_L3 * PTRS_PER_PGD / 2)
#ifdef CONFIG_COMPAT #define TASK_SIZE_32 (_AC(0x80000000, UL) - PAGE_SIZE) #define TASK_SIZE (test_thread_flag(TIF_32BIT) ? \ TASK_SIZE_32 : TASK_SIZE_64) #else [...]
Meaning CONFIG_COMPAT is only available in CONFIG_64BIT, and TASK_SIZE in compat mode is either TASK_SIZE_32 or TASK_SIZE_64 depending on the thread_flag.
from processor.h: #ifdef CONFIG_64BIT #define DEFAULT_MAP_WINDOW (UL(1) << (MMAP_VA_BITS - 1)) #define STACK_TOP_MAX TASK_SIZE_64 [...] #define STACK_TOP DEFAULT_MAP_WINDOW
where: #define MMAP_VA_BITS (is_compat_task() ? VA_BITS_SV32 : MMAP_VA_BITS_64) with MMAP_VA_BITS_64 being either 48 or 37.
In compat mode, STACK_TOP = 1 << (32 - 1) -> 0x80000000 TASK_SIZE = 0x8000000 - 4k -> 0x7ffff000
IIUC, your suggestion is to make TASK_SIZE = STACK_TOP in compat mode only.
Then why not: #ifdef CONFIG_COMPAT #define TASK_SIZE_32 STACK_TOP
With some comments explaining why there is no need to reserve a PAGE_SIZE in the TASK_SIZE_32.
Does that make sense?
Thanks! Leo
> > Freeing unused kernel image (initmem) memory: 2236K > Run /sbin/init as init process > Starting init: /sbin/init exists but couldn't execute it (error -14) > Run /etc/init as init process > ... > > Cc: stable@vger.kernel.org > Fixes: add2cc6b6515 ("RISC-V: mm: Restrict address space for sv39,sv48,sv57") > Signed-off-by: Guo Ren <guoren@linux.alibaba.com> > Signed-off-by: Guo Ren <guoren@kernel.org> > --- > arch/riscv/include/asm/pgtable.h | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/arch/riscv/include/asm/pgtable.h b/arch/riscv/include/asm/pgtable.h > index ab00235b018f..74ffb2178f54 100644 > --- a/arch/riscv/include/asm/pgtable.h > +++ b/arch/riscv/include/asm/pgtable.h > @@ -881,7 +881,7 @@ static inline pte_t pte_swp_clear_exclusive(pte_t pte) > #define TASK_SIZE_MIN (PGDIR_SIZE_L3 * PTRS_PER_PGD / 2) > > #ifdef CONFIG_COMPAT > -#define TASK_SIZE_32 (_AC(0x80000000, UL) - PAGE_SIZE) > +#define TASK_SIZE_32 (_AC(0x80000000, UL))
> #define TASK_SIZE (test_thread_flag(TIF_32BIT) ? \ > TASK_SIZE_32 : TASK_SIZE_64) > #else > -- > 2.40.1 >
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