From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from foss.arm.com ([217.140.101.70]:39854 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S933501AbeGFQiF (ORCPT ); Fri, 6 Jul 2018 12:38:05 -0400 Date: Fri, 6 Jul 2018 17:38:45 +0100 From: Will Deacon To: Mark Rutland Cc: linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, catalin.marinas@arm.com, dave.martin@arm.com, hch@infradead.org, james.morse@arm.com, linux@dominikbrodowski.net, linux-fsdevel@vger.kernel.org, marc.zyngier@arm.com, viro@zeniv.linux.org.uk Subject: Re: [PATCHv4 11/19] arm64: don't reload GPRs after apply_ssbd Message-ID: <20180706163844.GB27483@arm.com> References: <20180702110415.10465-1-mark.rutland@arm.com> <20180702110415.10465-12-mark.rutland@arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180702110415.10465-12-mark.rutland@arm.com> Sender: linux-fsdevel-owner@vger.kernel.org List-ID: On Mon, Jul 02, 2018 at 12:04:07PM +0100, Mark Rutland wrote: > Now that all of the syscall logic works on the saved pt_regs, apply_ssbd > can safely corrupt x0-x3 in the entry paths, and we no longer need to > restore them. So let's remove the logic doing so. > > With that logic gone, we can fold the branch target into the macro, so > that callers need not deal with this. GAS provides \@, which provides a > unique value per macro invocation, which we can use to create a unique > label. > > Signed-off-by: Mark Rutland > Acked-by: Marc Zyngier > Acked-by: Catalin Marinas > Cc: Will Deacon > --- > arch/arm64/kernel/entry.S | 20 +++++++------------- > 1 file changed, 7 insertions(+), 13 deletions(-) > > diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S > index c41b84d06644..728bc7cc5bbb 100644 > --- a/arch/arm64/kernel/entry.S > +++ b/arch/arm64/kernel/entry.S > @@ -130,20 +130,21 @@ alternative_else_nop_endif > > // This macro corrupts x0-x3. It is the caller's duty > // to save/restore them if required. > - .macro apply_ssbd, state, targ, tmp1, tmp2 > + .macro apply_ssbd, state, tmp1, tmp2 > #ifdef CONFIG_ARM64_SSBD > alternative_cb arm64_enable_wa2_handling > - b \targ > + b skip_apply_ssbd\@ > alternative_cb_end > ldr_this_cpu \tmp2, arm64_ssbd_callback_required, \tmp1 > - cbz \tmp2, \targ > + cbz \tmp2, skip_apply_ssbd\@ > ldr \tmp2, [tsk, #TSK_TI_FLAGS] > - tbnz \tmp2, #TIF_SSBD, \targ > + tbnz \tmp2, #TIF_SSBD, skip_apply_ssbd\@ Talking to Dave, he makes a good point that this is pretty fragile if a macro expansion within the macro itself uses \@, since this would result in an unexpected label update and everything would go wrong. Can you default initialise an extra label argument to \@, or does that not work? Will