From: Haiyue Wang <haiyue.wang@intel.com>
To: bpf@vger.kernel.org
Cc: Haiyue Wang <haiyue.wang@intel.com>,
Alexei Starovoitov <ast@kernel.org>,
Daniel Borkmann <daniel@iogearbox.net>,
Andrii Nakryiko <andrii@kernel.org>,
Martin KaFai Lau <martin.lau@linux.dev>,
Eduard Zingerman <eddyz87@gmail.com>, Song Liu <song@kernel.org>,
Yonghong Song <yonghong.song@linux.dev>,
John Fastabend <john.fastabend@gmail.com>,
KP Singh <kpsingh@kernel.org>,
Stanislav Fomichev <sdf@google.com>, Hao Luo <haoluo@google.com>,
Jiri Olsa <jolsa@kernel.org>,
linux-kernel@vger.kernel.org (open list)
Subject: [PATCH bpf-next v1] bpf,arena: Remove redundant page mask of vmf->address
Date: Tue, 7 May 2024 14:33:39 +0800 [thread overview]
Message-ID: <20240507063358.8048-1-haiyue.wang@intel.com> (raw)
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>
---
kernel/bpf/arena.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/kernel/bpf/arena.c b/kernel/bpf/arena.c
index 343c3456c8dd..1876dc7ebb57 100644
--- 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);
--
2.43.2
next reply other threads:[~2024-05-07 6:29 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-05-07 6:33 Haiyue Wang [this message]
2024-05-07 21:20 ` [PATCH bpf-next v1] bpf,arena: Remove redundant page mask of vmf->address patchwork-bot+netdevbpf
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