From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 8CB6F53B7 for ; Wed, 9 Aug 2023 11:14:48 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 0EB4EC433C7; Wed, 9 Aug 2023 11:14:47 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1691579688; bh=IInDt4kWTBBXfokco1nrpq7DW+BCTjLU+UOPb9o0vyo=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=Hh5QYeOPJ1gydfHiI5raz1H1XOX6l9B2IeTDQ1x+QZ91PipSPRYpbt0m2R/9/OylZ Dn1yvfRyysvOZjfb+JB1DIjiG8bjHUgAROUYjkIrZr4xBin53h2aggnv9yH4PTG6Ej IZsm1B9aFmxp7BxvvKeOsBNWi+o8SM1apxFImdY4= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Vineet Gupta , Sasha Levin Subject: [PATCH 4.19 081/323] ARCv2: entry: push out the Z flag unclobber from common EXCEPTION_PROLOGUE Date: Wed, 9 Aug 2023 12:38:39 +0200 Message-ID: <20230809103701.835650896@linuxfoundation.org> X-Mailer: git-send-email 2.41.0 In-Reply-To: <20230809103658.104386911@linuxfoundation.org> References: <20230809103658.104386911@linuxfoundation.org> User-Agent: quilt/0.67 Precedence: bulk X-Mailing-List: patches@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit From: Vineet Gupta [ Upstream commit 23c0cbd0c75c3b564850294427fd2be2bc2a015b ] Upon a taken interrupt/exception from User mode, HS hardware auto sets Z flag. This helps shave a few instructions from EXCEPTION_PROLOGUE by eliding re-reading ERSTATUS and some bit fiddling. However TLB Miss Exception handler can clobber the CPU flags and still end up in EXCEPTION_PROLOGUE in the slow path handling TLB handling case: EV_TLBMissD do_slow_path_pf EV_TLBProtV (aliased to call_do_page_fault) EXCEPTION_PROLOGUE As a result, EXCEPTION_PROLOGUE need to "unclobber" the Z flag which this patch changes. It is now pushed out to TLB Miss Exception handler. The reasons beings: - The flag restoration is only needed for slowpath TLB Miss Exception handling, but currently being in EXCEPTION_PROLOGUE penalizes all exceptions such as ProtV and syscall Trap, where Z flag is already as expected. - Pushing unclobber out to where it was clobbered is much cleaner and also serves to document the fact. - Makes EXCEPTION_PROLGUE similar to INTERRUPT_PROLOGUE so easier to refactor the common parts which is what this series aims to do Signed-off-by: Vineet Gupta Stable-dep-of: 92e2921eeafd ("ARC: define ASM_NL and __ALIGN(_STR) outside #ifdef __ASSEMBLY__ guard") Signed-off-by: Sasha Levin --- arch/arc/include/asm/entry-arcv2.h | 8 -------- arch/arc/mm/tlbex.S | 11 +++++++++++ 2 files changed, 11 insertions(+), 8 deletions(-) diff --git a/arch/arc/include/asm/entry-arcv2.h b/arch/arc/include/asm/entry-arcv2.h index 1c3520d1fa420..3209a67629606 100644 --- a/arch/arc/include/asm/entry-arcv2.h +++ b/arch/arc/include/asm/entry-arcv2.h @@ -225,14 +225,6 @@ ; -- for interrupts, regs above are auto-saved by h/w in that order -- ; Now do what ISR prologue does (manually save r12, sp, fp, gp, r25) - ; - ; Set Z flag if this was from U mode (expected by INTERRUPT_PROLOGUE) - ; Although H/w exception micro-ops do set Z flag for U mode (just like - ; for interrupts), it could get clobbered in case we soft land here from - ; a TLB Miss exception handler (tlbex.S) - - and r10, r10, STATUS_U_MASK - xor.f 0, r10, STATUS_U_MASK INTERRUPT_PROLOGUE exception diff --git a/arch/arc/mm/tlbex.S b/arch/arc/mm/tlbex.S index 0e1e47a67c736..e50cac799a518 100644 --- a/arch/arc/mm/tlbex.S +++ b/arch/arc/mm/tlbex.S @@ -396,6 +396,17 @@ EV_TLBMissD_fast_ret: ; additional label for VDK OS-kit instrumentation ;-------- Common routine to call Linux Page Fault Handler ----------- do_slow_path_pf: +#ifdef CONFIG_ISA_ARCV2 + ; Set Z flag if exception in U mode. Hardware micro-ops do this on any + ; taken interrupt/exception, and thus is already the case at the entry + ; above, but ensuing code would have already clobbered. + ; EXCEPTION_PROLOGUE called in slow path, relies on correct Z flag set + + lr r2, [erstatus] + and r2, r2, STATUS_U_MASK + bxor.f 0, r2, STATUS_U_BIT +#endif + ; Restore the 4-scratch regs saved by fast path miss handler TLBMISS_RESTORE_REGS -- 2.39.2