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bpf: Allow specifying volatile type modifier for kptrs

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This is useful in particular to mark the pointer as volatile, so that
compiler treats each load and store to the field as a volatile access.
The alternative is having to define and use READ_ONCE and WRITE_ONCE in
the BPF program.

Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
Acked-by: David Vernet <void@manifault.com>
Link: https://lore.kernel.org/r/20221103191013.1236066-3-memxor@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
This commit is contained in:
Kumar Kartikeya Dwivedi 2022-11-04 00:39:51 +05:30 committed by Alexei Starovoitov
parent 9805af8d8a
commit 23da464dd6
2 changed files with 8 additions and 0 deletions
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5
include/linux/btf.h
View File

@ -288,6 +288,11 @@ static inline bool btf_type_is_typedef(const struct btf_type *t)
return BTF_INFO_KIND(t->info) == BTF_KIND_TYPEDEF;
}
static inline bool btf_type_is_volatile(const struct btf_type *t)
{
return BTF_INFO_KIND(t->info) == BTF_KIND_VOLATILE;
}
static inline bool btf_type_is_func(const struct btf_type *t)
{
return BTF_INFO_KIND(t->info) == BTF_KIND_FUNC;

3
kernel/bpf/btf.c
View File

@ -3225,6 +3225,9 @@ static int btf_find_kptr(const struct btf *btf, const struct btf_type *t,
enum bpf_kptr_type type;
u32 res_id;
/* Permit modifiers on the pointer itself */
if (btf_type_is_volatile(t))
t = btf_type_by_id(btf, t->type);
/* For PTR, sz is always == 8 */
if (!btf_type_is_ptr(t))
return BTF_FIELD_IGNORE;