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Message-ID: <CAJF2gTT=EQzsuYMHr3FLb82Gi325PqWMEOAzfc6fg=go+gKP_g@mail.gmail.com> Date: Fri, 22 Dec 2023 10:57:16 +0800 From: Guo Ren <guoren@...nel.org> To: Leonardo Bras <leobras@...hat.com> Cc: linux-kernel@...r.kernel.org, paul.walmsley@...ive.com, palmer@...belt.com, alexghiti@...osinc.com, charlie@...osinc.com, xiao.w.wang@...el.com, david@...hat.com, panqinglin2020@...as.ac.cn, rick.p.edgecombe@...el.com, willy@...radead.org, bjorn@...osinc.com, conor.dooley@...rochip.com, cleger@...osinc.com, linux-riscv@...ts.infradead.org, Guo Ren <guoren@...ux.alibaba.com>, stable@...r.kernel.org Subject: Re: [PATCH V2 1/4] riscv: mm: Fixup compat mode boot failure On Fri, Dec 22, 2023 at 9:51 AM Leonardo Bras <leobras@...hat.com> wrote: > > Hello Guo Ren, > > On Thu, Dec 21, 2023 at 10:46:58AM -0500, guoren@...nel.org wrote: > > From: Guo Ren <guoren@...ux.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. > > 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@...r.kernel.org > > Fixes: add2cc6b6515 ("RISC-V: mm: Restrict address space for sv39,sv48,sv57") > > Signed-off-by: Guo Ren <guoren@...ux.alibaba.com> > > Signed-off-by: Guo Ren <guoren@...nel.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
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