From: Ard Biesheuvel <ardb@kernel.org> mainline inclusion from mainline-v5.12-rc1 commit d13c613f136c category: bugfix issue: #I3ZXZF CVE: NA Reference: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?i... ----------------------------------------------- Add a macro cond_yield that branches to a specified label when called if the TIF_NEED_RESCHED flag is set and decreasing the preempt count would make the task preemptible again, resulting in a schedule to occur. This can be used by kernel mode SIMD code that keeps a lot of state in SIMD registers, which would make chunking the input in order to perform the cond_resched() check from C code disproportionately costly. Signed-off-by: Ard Biesheuvel <ardb@kernel.org> Link: https://lore.kernel.org/r/20210203113626.220151-2-ardb@kernel.org Signed-off-by: Will Deacon <will@kernel.org> Signed-off-by: Wei Li <liwei391@huawei.com> Reviewed-by: Jason Yan <yanaijie@huawei.com> Reviewed-by: Hanjun Guo <guohanjun@huawei.com> Signed-off-by: Chen Jun <chenjun102@huawei.com> Signed-off-by: Yu Changchun <yuchangchun1@huawei.com> --- arch/arm64/include/asm/assembler.h | 16 ++++++++++++++++ 1 file changed, 16 insertions(+) diff --git a/arch/arm64/include/asm/assembler.h b/arch/arm64/include/asm/assembler.h index ddbe6bf00e33..f1838bd93a40 100644 --- a/arch/arm64/include/asm/assembler.h +++ b/arch/arm64/include/asm/assembler.h @@ -745,6 +745,22 @@ USER(\label, ic ivau, \tmp2) // invalidate I line PoU .Lyield_out_\@ : .endm + /* + * Check whether preempt-disabled code should yield as soon as it + * is able. This is the case if re-enabling preemption a single + * time results in a preempt count of zero, and the TIF_NEED_RESCHED + * flag is set. (Note that the latter is stored negated in the + * top word of the thread_info::preempt_count field) + */ + .macro cond_yield, lbl:req, tmp:req +#ifdef CONFIG_PREEMPTION + get_current_task \tmp + ldr \tmp, [\tmp, #TSK_TI_PREEMPT] + sub \tmp, \tmp, #PREEMPT_DISABLE_OFFSET + cbz \tmp, \lbl +#endif + .endm + /* * This macro emits a program property note section identifying * architecture features which require special handling, mainly for -- 2.22.0