On Fri, Dec 22, 2023 at 01:23:29AM -0300, Leonardo Bras wrote:
On Thu, Dec 21, 2023 at 08:04:43PM -0800, Charlie Jenkins wrote:
On Fri, Dec 22, 2023 at 12:34:56AM -0300, Leonardo Bras wrote:
On Thu, Dec 21, 2023 at 10:46:59AM -0500, guoren@kernel.org wrote:
From: Guo Ren guoren@linux.alibaba.com
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@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/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.
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)
I agree, this change does not make sense for compat mode. Compat mode should never return an address that is greater than 2^32, but this change allows that.
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.
That is not the case. I documented this behavior and reasoning in Documentation/arch/riscv/vm-layout.rst in the "Userspace VAs" section.
I can reiterate here though. The hint address to mmap (defined here as "addr") is the maximum userspace address that mmap should provide. What you are describing is a minimum. The purpose of this change was to allow applications that are not compatible with a larger virtual address (such as applications like Java that use the upper bits of the VA to store data) to have a consistent way of specifying how many bits they would like to be left free in the VA. This requires to take the next lowest address space to guaruntee that all of the most-significant bits left clear in hint address do not end up populated in the virtual address returned by mmap.
- Charlie
Hello Charlie, thank you for helping me understand!
Ok, that does make sense now! The addr value hints "don't allocate > addr" and thus:
- 0 < addr < 2^48 : mmap_end = 2^39
- 2^48 < addr < 2^57: mmap_end = 2^48
Ok, but then
- addr > 2^57: mmap_end = 2^57
right?
I mean, probably STACK_TOP_MAX in non-compat mode means 2^57 already, but having it explicitly like:
else if ((_addr) >= VA_USER_SV57) \ mmap_end = VA_USER_SV57; \
would not be better for a future full 64-bit addressing? (since it's already on a different if clause)
I agree, that does make more sense.
I could add comment on top of the macro with a short version on your addr hint description above. Would that be ok?
Sure :)
- Charlie
Thanks! Leo
Do I get it wrong?
(I will send an RFC 'fixing' the code the way I am whinking it should look like)
Thanks, Leo
-- 2.40.1