On Thu, Dec 21, 2023 at 07:50:27PM -0800, Charlie Jenkins wrote:
On Fri, Dec 22, 2023 at 10:57:16AM +0800, Guo Ren wrote:
On Fri, Dec 22, 2023 at 9:51 AM Leonardo Bras leobras@redhat.com wrote:
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.
Yes, it causes the problem, which causes the boot to fail.
I think what Leonardo is getting at is that it is odd that it would cause boot issues if TASK_SIZE is not equal STACK_TOP. This seems indicative of a different problem. While this may fix the issue, it should be valid for TASK_SIZE to be less than STACK_TOP.
- Charlie
That is also a good point, but I am not that acquainted to this to actually propose this.
I was thinking more on these questions: Is TASK_SIZE and STACK_TOP related somehow? If so, would not be better to describe one in terms of the other, like #define TASK_SIZE (STACK_TOP - PAGE_SIZE)
Or the other way around.
I mean, if they have any relation it would be much easier to represent them that way, and it would avoid having two magical numbers.
Thanks! Leo
Then why not: #ifdef CONFIG_COMPAT #define TASK_SIZE_32 STACK_TOP
Yes, it's the solution that I think at first. But I didn't find any problem with 0x7ffff000 ~ 0x80000000, and then I removed this gap to unify it with Sv39 and Sv48.
With some comments explaining why there is no need to reserve a PAGE_SIZE in the TASK_SIZE_32.
At first, I wanted to put a invalid page between the user & kernel space, but it seems useless.
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
-- Best Regards Guo Ren