On Thu, Jul 20, 2023 at 10:13:54AM +0200, Alexandre Ghiti wrote:
On Fri, Jul 14, 2023 at 6:55 PM Charlie Jenkins charlie@rivosinc.com wrote:
Make sv48 the default address space for mmap as some applications currently depend on this assumption. A hint address passed to mmap will cause the largest address space that fits entirely into the hint to be used. If the hint is less than or equal to 1<<38, an sv39 address will be used. An exception is that if the hint address is 0, then a sv48 address will be used. After an address space is completely full, the next smallest address space will be used.
Signed-off-by: Charlie Jenkins charlie@rivosinc.com
arch/riscv/include/asm/elf.h | 2 +- arch/riscv/include/asm/pgtable.h | 12 +++++++- arch/riscv/include/asm/processor.h | 46 +++++++++++++++++++++++++----- 3 files changed, 51 insertions(+), 9 deletions(-)
diff --git a/arch/riscv/include/asm/elf.h b/arch/riscv/include/asm/elf.h index c24280774caf..5d3368d5585c 100644 --- a/arch/riscv/include/asm/elf.h +++ b/arch/riscv/include/asm/elf.h @@ -49,7 +49,7 @@ extern bool compat_elf_check_arch(Elf32_Ehdr *hdr);
- the loader. We need to make sure that it is out of the way of the program
- that it will "exec", and that there is sufficient room for the brk.
*/ -#define ELF_ET_DYN_BASE ((TASK_SIZE / 3) * 2) +#define ELF_ET_DYN_BASE ((DEFAULT_MAP_WINDOW / 3) * 2)
#ifdef CONFIG_64BIT #ifdef CONFIG_COMPAT diff --git a/arch/riscv/include/asm/pgtable.h b/arch/riscv/include/asm/pgtable.h index 75970ee2bda2..e13f5872bfe9 100644 --- a/arch/riscv/include/asm/pgtable.h +++ b/arch/riscv/include/asm/pgtable.h @@ -63,12 +63,22 @@
- position vmemmap directly below the VMALLOC region.
*/ #ifdef CONFIG_64BIT +#define VA_BITS_SV39 39 +#define VA_BITS_SV48 48 +#define VA_BITS_SV57 57
+#define VA_USER_SV39 (UL(1) << (VA_BITS_SV39 - 1)) +#define VA_USER_SV48 (UL(1) << (VA_BITS_SV48 - 1)) +#define VA_USER_SV57 (UL(1) << (VA_BITS_SV57 - 1))
#define VA_BITS (pgtable_l5_enabled ? \
57 : (pgtable_l4_enabled ? 48 : 39))
VA_BITS_SV57 : (pgtable_l4_enabled ? VA_BITS_SV48 : VA_BITS_SV39))#else #define VA_BITS 32 #endif
+#define MMAP_VA_BITS ((VA_BITS >= VA_BITS_SV48) ? VA_BITS_SV48 : VA_BITS)
#define VMEMMAP_SHIFT \ (VA_BITS - PAGE_SHIFT - 1 + STRUCT_PAGE_MAX_SHIFT) #define VMEMMAP_SIZE BIT(VMEMMAP_SHIFT) diff --git a/arch/riscv/include/asm/processor.h b/arch/riscv/include/asm/processor.h index c950a8d9edef..14a5396eed3d 100644 --- a/arch/riscv/include/asm/processor.h +++ b/arch/riscv/include/asm/processor.h @@ -13,20 +13,52 @@
#include <asm/ptrace.h>
-/*
- This decides where the kernel will search for a free chunk of vm
- space during mmap's.
- */
-#define TASK_UNMAPPED_BASE PAGE_ALIGN(TASK_SIZE / 3)
-#define STACK_TOP TASK_SIZE #ifdef CONFIG_64BIT +#define DEFAULT_MAP_WINDOW (UL(1) << (MMAP_VA_BITS - 1)) #define STACK_TOP_MAX TASK_SIZE_64
+#define arch_get_mmap_end(addr, len, flags) \ +({ \
unsigned long mmap_end; \if ((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; \else if ((addr) == 0) \mmap_end = DEFAULT_MAP_WINDOW; \else \mmap_end = VA_USER_SV39; \mmap_end; \+})
What about the following instead:
#define arch_get_mmap_end(addr, len, flags) \ ({ \ unsigned long mmap_end; \ if ((addr) >= VA_USER_SV57) \ mmap_end = STACK_TOP_MAX; \ // Maybe a comment here that says it returns the max user address of the current mode, not obvious at first sight. else \ mmap_end = DEFAULT_MAP_WINDOW; \ mmap_end; \ })
The only corner case is when sv57 is active, then only a hint greater than VA_USER_SV57 can return a sv57 user address. Otherwise, we just need to return the default mmap end right?
+#define arch_get_mmap_base(addr, base) \ +({ \
unsigned long mmap_base; \if (((addr) >= VA_USER_SV57) && (VA_BITS >= VA_BITS_SV57)) \mmap_base = (base) + (VA_USER_SV57 - DEFAULT_MAP_WINDOW); \else if ((((addr) >= VA_USER_SV48)) && (VA_BITS >= VA_BITS_SV48)) \mmap_base = (base) + (VA_USER_SV48 - DEFAULT_MAP_WINDOW); \else if ((addr) == 0) \mmap_base = (base); \else \mmap_base = (base) + (VA_USER_SV39 - DEFAULT_MAP_WINDOW); \mmap_base; \+})
From arch_pick_mmap_layout() (https://elixir.bootlin.com/linux/latest/source/mm/util.c#L433), the "base" argument is:
- either STACK_TOP in top-down (more or less some random offset)
- or TASK_UNMAPPED_BASE in bottom-up (more or less some random offset)
When bottom-up is the current mode, we should not change the base, so adding (VA_USER_SV57 - DEFAULT_MAP_WINDOW) in the first case is not right for me. When sv48 or sv57 are the active mode, DEFAULT_MAP_WINDOW is equal to VA_USER_SV48 right? So (VA_USER_SV48 - DEFAULT_MAP_WINDOW) is 0, so not useful. And for the last case, when the user asks for a sv39 address whereas the active mode is sv48 or sv57, then (VA_USER_SV39 - DEFAULT_MAP_WINDOW) is negative and the base is smaller which is not correct.
In the bottom-up case mm->mmap_base is directly used instead of arch_get_mmap_base so base will not be modified in that case. The math here is confusing so I can refactor it. I like your suggestion to extract out the rnd value of base with (base) - DEFAULT_MAP_WINDOW since base is defined as PAGE_ALIGN(STACK_TOP - gap - rnd) and STACK_TOP is DEFAULT_MAP_WINDOW. This (-gap-rnd) value can then directly be used instead of redoing the math in each if.
In the bottom-up case, we should preserve the base and I think that again, only sv57 is the corner case to deal with.
For both this comment and the one above, I think we should allow the user to default back to sv38. I talked to Palmer and he would prefer allowing selection of sv38. Since there is no overhead, there is no need to prevent the user from doing so.
#else +#define DEFAULT_MAP_WINDOW TASK_SIZE #define STACK_TOP_MAX TASK_SIZE #endif #define STACK_ALIGN 16
+#define STACK_TOP DEFAULT_MAP_WINDOW
+/*
- This decides where the kernel will search for a free chunk of vm
- space during mmap's.
- */
+#define TASK_UNMAPPED_BASE PAGE_ALIGN(DEFAULT_MAP_WINDOW / 3)
#ifndef __ASSEMBLY__
struct task_struct;
2.41.0