On Fri, Dec 22, 2023 at 12:04 PM Charlie Jenkins charlie@rivosinc.com 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.
#define STACK_TOP_MAX TASK_SIZE #define TASK_SIZE (is_compat_task() ? TASK_SIZE_32 : TASK_SIZE_64)
So, this change limits an address in 2^32 for compat mode, and your patch broke the rule. So that is why we need this patch to fix up.
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
Yes, I agree with this change and use Zjpm with PLEN=48 to optimize them in the future.
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
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