diff mbox series

[bpf-next] xsk: Elide base_addr comparison in xp_unaligned_validate_desc

Message ID 20230406212136.19716-1-kal.conley@dectris.com (mailing list archive)
State Superseded
Delegated to: BPF
Headers show
Series [bpf-next] xsk: Elide base_addr comparison in xp_unaligned_validate_desc | expand

Checks

Context Check Description
netdev/series_format success Single patches do not need cover letters
netdev/tree_selection success Clearly marked for bpf-next
netdev/fixes_present success Fixes tag not required for -next series
netdev/header_inline success No static functions without inline keyword in header files
netdev/build_32bit success Errors and warnings before: 20 this patch: 20
netdev/cc_maintainers success CCed 14 of 14 maintainers
netdev/build_clang success Errors and warnings before: 18 this patch: 18
netdev/verify_signedoff success Signed-off-by tag matches author and committer
netdev/deprecated_api success None detected
netdev/check_selftest success No net selftest shell script
netdev/verify_fixes success No Fixes tag
netdev/build_allmodconfig_warn success Errors and warnings before: 20 this patch: 20
netdev/checkpatch success total: 0 errors, 0 warnings, 0 checks, 20 lines checked
netdev/kdoc success Errors and warnings before: 0 this patch: 0
netdev/source_inline success Was 0 now: 0
bpf/vmtest-bpf-next-PR success PR summary
bpf/vmtest-bpf-next-VM_Test-10 success Logs for test_maps on s390x with gcc
bpf/vmtest-bpf-next-VM_Test-1 success Logs for ShellCheck
bpf/vmtest-bpf-next-VM_Test-2 success Logs for build for aarch64 with gcc
bpf/vmtest-bpf-next-VM_Test-3 success Logs for build for aarch64 with llvm-16
bpf/vmtest-bpf-next-VM_Test-4 success Logs for build for s390x with gcc
bpf/vmtest-bpf-next-VM_Test-5 success Logs for build for x86_64 with gcc
bpf/vmtest-bpf-next-VM_Test-6 success Logs for build for x86_64 with llvm-16
bpf/vmtest-bpf-next-VM_Test-7 success Logs for set-matrix
bpf/vmtest-bpf-next-VM_Test-8 success Logs for test_maps on aarch64 with gcc
bpf/vmtest-bpf-next-VM_Test-9 success Logs for test_maps on aarch64 with llvm-16
bpf/vmtest-bpf-next-VM_Test-11 success Logs for test_maps on x86_64 with gcc
bpf/vmtest-bpf-next-VM_Test-12 success Logs for test_maps on x86_64 with llvm-16
bpf/vmtest-bpf-next-VM_Test-13 success Logs for test_progs on aarch64 with gcc
bpf/vmtest-bpf-next-VM_Test-14 success Logs for test_progs on aarch64 with llvm-16
bpf/vmtest-bpf-next-VM_Test-15 success Logs for test_progs on s390x with gcc
bpf/vmtest-bpf-next-VM_Test-16 success Logs for test_progs on x86_64 with gcc
bpf/vmtest-bpf-next-VM_Test-17 success Logs for test_progs on x86_64 with llvm-16
bpf/vmtest-bpf-next-VM_Test-18 success Logs for test_progs_no_alu32 on aarch64 with gcc
bpf/vmtest-bpf-next-VM_Test-19 success Logs for test_progs_no_alu32 on aarch64 with llvm-16
bpf/vmtest-bpf-next-VM_Test-20 fail Logs for test_progs_no_alu32 on s390x with gcc
bpf/vmtest-bpf-next-VM_Test-21 success Logs for test_progs_no_alu32 on x86_64 with gcc
bpf/vmtest-bpf-next-VM_Test-22 success Logs for test_progs_no_alu32 on x86_64 with llvm-16
bpf/vmtest-bpf-next-VM_Test-23 success Logs for test_progs_no_alu32_parallel on aarch64 with gcc
bpf/vmtest-bpf-next-VM_Test-24 success Logs for test_progs_no_alu32_parallel on aarch64 with llvm-16
bpf/vmtest-bpf-next-VM_Test-25 success Logs for test_progs_no_alu32_parallel on x86_64 with gcc
bpf/vmtest-bpf-next-VM_Test-26 success Logs for test_progs_no_alu32_parallel on x86_64 with llvm-16
bpf/vmtest-bpf-next-VM_Test-27 success Logs for test_progs_parallel on aarch64 with gcc
bpf/vmtest-bpf-next-VM_Test-28 success Logs for test_progs_parallel on aarch64 with llvm-16
bpf/vmtest-bpf-next-VM_Test-29 success Logs for test_progs_parallel on x86_64 with gcc
bpf/vmtest-bpf-next-VM_Test-30 success Logs for test_progs_parallel on x86_64 with llvm-16
bpf/vmtest-bpf-next-VM_Test-31 success Logs for test_verifier on aarch64 with gcc
bpf/vmtest-bpf-next-VM_Test-32 success Logs for test_verifier on aarch64 with llvm-16
bpf/vmtest-bpf-next-VM_Test-33 success Logs for test_verifier on s390x with gcc
bpf/vmtest-bpf-next-VM_Test-34 success Logs for test_verifier on x86_64 with gcc
bpf/vmtest-bpf-next-VM_Test-35 success Logs for test_verifier on x86_64 with llvm-16

Commit Message

Kal Cutter Conley April 6, 2023, 9:21 p.m. UTC 
Remove redundant (base_addr >= pool->addrs_cnt) comparison from the
conditional.

In particular, addr is computed as:

    addr = base_addr + offset

where base_addr and offset are stored as 48-bit and 16-bit unsigned
integers, respectively. The above sum cannot overflow u64 since
base_addr has a maximum value of 0x0000ffffffffffff and offset has a
maximum value of 0xffff (implying a maximum sum of 0x000100000000fffe).
Since overflow is impossible, it follows that addr >= base_addr.

Now if (base_addr >= pool->addrs_cnt), then clearly:

    addr >= base_addr
         >= pool->addrs_cnt

Thus, (base_addr >= pool->addrs_cnt) implies (addr >= pool->addrs_cnt).
Subsequently, the former comparison is unnecessary in the conditional
since for any boolean expressions A and B, (A || B) && (A -> B) is
equivalent to B.

Signed-off-by: Kal Conley <kal.conley@dectris.com>
---
 net/xdp/xsk_queue.h | 10 ++++------
 1 file changed, 4 insertions(+), 6 deletions(-)

Comments

Kal Cutter Conley April 9, 2023, 2:54 p.m. UTC | #1 
> +       addr = xp_unaligned_add_offset_to_addr(desc->addr);
> +

I guess this assignment should simply be combined with the variable
declaration. This will shorten the function by an additional two lines
of code.
diff mbox series

Patch

diff --git a/net/xdp/xsk_queue.h b/net/xdp/xsk_queue.h
index 66c6f57c9c44..016f3753180a 100644
--- a/net/xdp/xsk_queue.h
+++ b/net/xdp/xsk_queue.h
@@ -153,16 +153,14 @@  static inline bool xp_aligned_validate_desc(struct xsk_buff_pool *pool,
 static inline bool xp_unaligned_validate_desc(struct xsk_buff_pool *pool,
 					      struct xdp_desc *desc)
 {
-	u64 addr, base_addr;
-
-	base_addr = xp_unaligned_extract_addr(desc->addr);
-	addr = xp_unaligned_add_offset_to_addr(desc->addr);
+	u64 addr;
 
 	if (desc->len > pool->chunk_size)
 		return false;
 
-	if (base_addr >= pool->addrs_cnt || addr >= pool->addrs_cnt ||
-	    addr + desc->len > pool->addrs_cnt ||
+	addr = xp_unaligned_add_offset_to_addr(desc->addr);
+
+	if (addr >= pool->addrs_cnt || addr + desc->len > pool->addrs_cnt ||
 	    xp_desc_crosses_non_contig_pg(pool, addr, desc->len))
 		return false;