On Fri, Dec 22, 2023 at 12:26:19PM +0800, Guo Ren wrote:
> On Fri, Dec 22, 2023 at 11:35 AM Leonardo Bras <leobras@xxxxxxxxxx> wrote:
> >
> > On Thu, Dec 21, 2023 at 10:46:59AM -0500, guoren@xxxxxxxxxx wrote:
> > > From: Guo Ren <guoren@xxxxxxxxxxxxxxxxx>
> > >
> > > When the task is in COMPAT mode, the arch_get_mmap_end should be 2GB,
> > > not TASK_SIZE_64. The TASK_SIZE has contained is_compat_mode()
> > > detection, so change the definition of STACK_TOP_MAX to TASK_SIZE
> > > directly.
> >
> > ok
> >
> > >
> > > Cc: stable@xxxxxxxxxxxxxxx
> > > Fixes: add2cc6b6515 ("RISC-V: mm: Restrict address space for sv39,sv48,sv57")
> > > Signed-off-by: Guo Ren <guoren@xxxxxxxxxxxxxxxxx>
> > > Signed-off-by: Guo Ren <guoren@xxxxxxxxxx>
> > > ---
> > > arch/riscv/include/asm/processor.h | 6 ++----
> > > 1 file changed, 2 insertions(+), 4 deletions(-)
> > >
> > > diff --git a/arch/riscv/include/asm/processor.h b/arch/riscv/include/asm/processor.h
> > > index f19f861cda54..1f538fc4448d 100644
> > > --- a/arch/riscv/include/asm/processor.h
> > > +++ b/arch/riscv/include/asm/processor.h
> > > @@ -16,15 +16,13 @@
> > >
> > > #ifdef CONFIG_64BIT
> > > #define DEFAULT_MAP_WINDOW (UL(1) << (MMAP_VA_BITS - 1))
> > > -#define STACK_TOP_MAX TASK_SIZE_64
> > > +#define STACK_TOP_MAX TASK_SIZE
> >
> > It means STACK_TOP_MAX will be in 64BIT:
> > - TASK_SIZE_32 if compat_mode=y
> > - TASK_SIZE_64 if compat_mode=n
> >
> > Makes sense for me.
> >
> > >
> > > #define arch_get_mmap_end(addr, len, flags) \
> > > ({ \
> > > unsigned long mmap_end; \
> > > typeof(addr) _addr = (addr); \
> > > - if ((_addr) == 0 || (IS_ENABLED(CONFIG_COMPAT) && is_compat_task())) \
> > > - mmap_end = STACK_TOP_MAX; \
> > > - else if ((_addr) >= VA_USER_SV57) \
> > > + if ((_addr) == 0 || (_addr) >= VA_USER_SV57) \
> > > mmap_end = STACK_TOP_MAX; \
> > > else if ((((_addr) >= VA_USER_SV48)) && (VA_BITS >= VA_BITS_SV48)) \
> > > mmap_end = VA_USER_SV48; \
> >
> >
> > I don't think I got this change, or how it's connected to the commit msg.
> The above is just code simplification; if STACK_TOP_MAX is TASK_SIZE, then
>
> if ((_addr) == 0 || (IS_ENABLED(CONFIG_COMPAT) && is_compat_task())) \
> mmap_end = STACK_TOP_MAX; \
> else if ((_addr) >= VA_USER_SV57) \
>
> is equal to:
>
> if ((_addr) == 0 || (_addr) >= VA_USER_SV57) \
I am failing to understand exactly how are they equal.
I mean, what in your STACK_TOP_MAX change made them equal?
See below, the behavior changed:
>
> >
> > Before:
> > - addr == 0, or addr > 2^57, or compat: mmap_end = STACK_TOP_MAX
> > - 2^48 < addr < 2^57: mmap_end = 2^48
> > - 0 < addr < 2^48 : mmap_end = 2^39
> >
> > Now:
> > - addr == 0, or addr > 2^57: mmap_end = STACK_TOP_MAX
> > - 2^48 < addr < 2^57: mmap_end = 2^48
> > - 0 < addr < 2^48 : mmap_end = 2^39
> >
> > IIUC compat mode addr will be < 2^32, so will always have mmap_end = 2^39
> > if addr != 0. Is that desireable?
> > (if not, above change is unneeded)
> >
^
With your change on STACK_TOP_MAX only (not changing arch_get_mmap_end),
you would have:
- compat_mode & (0 < addr < 2^32) -> mmap_end = 2^32
- non-compat, addr == 0, or addr > 2^57 -> mmap_end = TASK_SIZE_64
- non-compat, (2^48 < addr < 2^57) -> mmap_end = 2^48
- non-compat, (0 < addr < 2^48) -> mmap_end = 2^39
Which seems more likely, based on Charlie comments.
Thanks,
Leo
> > Also, unrelated to the change:
> > - 2^48 < addr < 2^57: mmap_end = 2^48
> > Is the above correct?
> > It looks like it should be 2^57 instead, and a new if clause for
> > 2^32 < addr < 2^48 should have mmap_end = 2^48.
> >
> > Do I get it wrong?
> Maybe I should move this into the optimization part.
>
> >
> > (I will send an RFC 'fixing' the code the way I am whinking it should look
> > like)
> >
> > Thanks,
> > Leo
> >
> >
> >
> >
> >
> > > --
> > > 2.40.1
> > >
> >
>
>
> --
> Best Regards
> Guo Ren
>
