3c2611bac0
LLVM commit https://reviews.llvm.org/D143726 introduced hoistMinMax optimization that transformed (i < VIRTIO_MAX_SGS) && (i < out_sgs) into i < MIN(VIRTIO_MAX_SGS, out_sgs) and caused the verifier to stop recognizing such loop as bounded. Which resulted in the following test failure: libbpf: prog 'trace_virtqueue_add_sgs': BPF program load failed: Bad address libbpf: prog 'trace_virtqueue_add_sgs': -- BEGIN PROG LOAD LOG -- The sequence of 8193 jumps is too complex. verification time 789206 usec stack depth 56 processed 156446 insns (limit 1000000) max_states_per_insn 7 total_states 1746 peak_states 1701 mark_read 12 -- END PROG LOAD LOG -- libbpf: prog 'trace_virtqueue_add_sgs': failed to load: -14 libbpf: failed to load object 'loop6.bpf.o' Workaround the verifier limitation for now with inline asm that prevents this particular optimization. Signed-off-by: Alexei Starovoitov <ast@kernel.org>
102 lines
2.2 KiB
C
102 lines
2.2 KiB
C
// SPDX-License-Identifier: GPL-2.0
|
|
|
|
#include <linux/ptrace.h>
|
|
#include <stddef.h>
|
|
#include <linux/bpf.h>
|
|
#include <bpf/bpf_helpers.h>
|
|
#include <bpf/bpf_tracing.h>
|
|
#include "bpf_misc.h"
|
|
|
|
char _license[] SEC("license") = "GPL";
|
|
|
|
/* typically virtio scsi has max SGs of 6 */
|
|
#define VIRTIO_MAX_SGS 6
|
|
|
|
/* Verifier will fail with SG_MAX = 128. The failure can be
|
|
* workarounded with a smaller SG_MAX, e.g. 10.
|
|
*/
|
|
#define WORKAROUND
|
|
#ifdef WORKAROUND
|
|
#define SG_MAX 10
|
|
#else
|
|
/* typically virtio blk has max SEG of 128 */
|
|
#define SG_MAX 128
|
|
#endif
|
|
|
|
#define SG_CHAIN 0x01UL
|
|
#define SG_END 0x02UL
|
|
|
|
struct scatterlist {
|
|
unsigned long page_link;
|
|
unsigned int offset;
|
|
unsigned int length;
|
|
};
|
|
|
|
#define sg_is_chain(sg) ((sg)->page_link & SG_CHAIN)
|
|
#define sg_is_last(sg) ((sg)->page_link & SG_END)
|
|
#define sg_chain_ptr(sg) \
|
|
((struct scatterlist *) ((sg)->page_link & ~(SG_CHAIN | SG_END)))
|
|
|
|
static inline struct scatterlist *__sg_next(struct scatterlist *sgp)
|
|
{
|
|
struct scatterlist sg;
|
|
|
|
bpf_probe_read_kernel(&sg, sizeof(sg), sgp);
|
|
if (sg_is_last(&sg))
|
|
return NULL;
|
|
|
|
sgp++;
|
|
|
|
bpf_probe_read_kernel(&sg, sizeof(sg), sgp);
|
|
if (sg_is_chain(&sg))
|
|
sgp = sg_chain_ptr(&sg);
|
|
|
|
return sgp;
|
|
}
|
|
|
|
static inline struct scatterlist *get_sgp(struct scatterlist **sgs, int i)
|
|
{
|
|
struct scatterlist *sgp;
|
|
|
|
bpf_probe_read_kernel(&sgp, sizeof(sgp), sgs + i);
|
|
return sgp;
|
|
}
|
|
|
|
int config = 0;
|
|
int result = 0;
|
|
|
|
SEC("kprobe/virtqueue_add_sgs")
|
|
int BPF_KPROBE(trace_virtqueue_add_sgs, void *unused, struct scatterlist **sgs,
|
|
unsigned int out_sgs, unsigned int in_sgs)
|
|
{
|
|
struct scatterlist *sgp = NULL;
|
|
__u64 length1 = 0, length2 = 0;
|
|
unsigned int i, n, len;
|
|
|
|
if (config != 0)
|
|
return 0;
|
|
|
|
for (i = 0; (i < VIRTIO_MAX_SGS) && (i < out_sgs); i++) {
|
|
__sink(out_sgs);
|
|
for (n = 0, sgp = get_sgp(sgs, i); sgp && (n < SG_MAX);
|
|
sgp = __sg_next(sgp)) {
|
|
bpf_probe_read_kernel(&len, sizeof(len), &sgp->length);
|
|
length1 += len;
|
|
n++;
|
|
}
|
|
}
|
|
|
|
for (i = 0; (i < VIRTIO_MAX_SGS) && (i < in_sgs); i++) {
|
|
__sink(in_sgs);
|
|
for (n = 0, sgp = get_sgp(sgs, i); sgp && (n < SG_MAX);
|
|
sgp = __sg_next(sgp)) {
|
|
bpf_probe_read_kernel(&len, sizeof(len), &sgp->length);
|
|
length2 += len;
|
|
n++;
|
|
}
|
|
}
|
|
|
|
config = 1;
|
|
result = length2 - length1;
|
|
return 0;
|
|
}
|