From: Christophe Leroy Date: Thu, 16 Sep 2021 14:52:09 +0000 (+0200) Subject: powerpc: warn on emulation of dcbz instruction in kernel mode X-Git-Url: http://git.maquefel.me/?a=commitdiff_plain;h=cbe654c779616807e1e6823c3bdbfe07a10562b8;p=linux.git powerpc: warn on emulation of dcbz instruction in kernel mode dcbz instruction shouldn't be used on non-cached memory. Using it on non-cached memory can result in alignment exception and implies a heavy handling. Instead of silentely emulating the instruction and resulting in high performance degradation, warn whenever an alignment exception is taken in kernel mode due to dcbz, so that the user is made aware that dcbz instruction has been used unexpectedly by the kernel. Reported-by: Stan Johnson Signed-off-by: Christophe Leroy Signed-off-by: Michael Ellerman Link: https://lore.kernel.org/r/2e3acfe63d289c6fba366e16973c9ab8369e8b75.1631803922.git.christophe.leroy@csgroup.eu --- diff --git a/arch/powerpc/kernel/align.c b/arch/powerpc/kernel/align.c index bbb4181621ddc..bf96b954a4eb2 100644 --- a/arch/powerpc/kernel/align.c +++ b/arch/powerpc/kernel/align.c @@ -349,6 +349,7 @@ int fix_alignment(struct pt_regs *regs) if (op.type != CACHEOP + DCBZ) return -EINVAL; PPC_WARN_ALIGNMENT(dcbz, regs); + WARN_ON_ONCE(!user_mode(regs)); r = emulate_dcbz(op.ea, regs); } else { if (type == LARX || type == STCX)