bpf: Remove redundant page mask of vmf->address

As the comment described in "struct vm_fault":
	".address"      : 'Faulting virtual address - masked'
	".real_address" : 'Faulting virtual address - unmasked'

The link [1] said: "Whatever the routes, all architectures end up to the
invocation of handle_mm_fault() which, in turn, (likely) ends up calling
__handle_mm_fault() to carry out the actual work of allocating the page
tables."

  __handle_mm_fault() does address assignment:
	.address = address & PAGE_MASK,
	.real_address = address,

This is debug dump by running `./test_progs -a "*arena*"`:

[   69.767494] arena fault: vmf->address = 10000001d000, vmf->real_address = 10000001d008
[   69.767496] arena fault: vmf->address = 10000001c000, vmf->real_address = 10000001c008
[   69.767499] arena fault: vmf->address = 10000001b000, vmf->real_address = 10000001b008
[   69.767501] arena fault: vmf->address = 10000001a000, vmf->real_address = 10000001a008
[   69.767504] arena fault: vmf->address = 100000019000, vmf->real_address = 100000019008
[   69.769388] arena fault: vmf->address = 10000001e000, vmf->real_address = 10000001e1e8

So we can use the value of 'vmf->address' to do BPF arena kernel address
space cast directly.

[1] https://docs.kernel.org/mm/page_tables.html

Signed-off-by: Haiyue Wang <haiyue.wang@intel.com>
Link: https://lore.kernel.org/r/20240507063358.8048-1-haiyue.wang@intel.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

diff --git a/kernel/bpf/arena.c b/kernel/bpf/arena.c
index 6c81630c52934e2754fab94b001ef67b3468db6d..f5953f1a95cd243eab5d57c170a9c4a2d99a222c 100644 (file)
--- a/kernel/bpf/arena.c
+++ b/kernel/bpf/arena.c
@@ -251,7 +251,7 @@ static vm_fault_t arena_vm_fault(struct vm_fault *vmf)
        int ret;
 
        kbase = bpf_arena_get_kern_vm_start(arena);
-       kaddr = kbase + (u32)(vmf->address & PAGE_MASK);
+       kaddr = kbase + (u32)(vmf->address);
 
        guard(mutex)(&arena->lock);
        page = vmalloc_to_page((void *)kaddr);