From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by smtp.subspace.kernel.org (Postfix) with ESMTP id 58A011953B0; Thu, 17 Oct 2024 07:44:23 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=217.140.110.172 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1729151064; cv=none; b=uV2Oo2jWk+s7RebHe8b3FsC63yokteLVsnvxE6JM1rAUJbv+3zj7CZV887BTYwCqkQBFQtVy7izah3nE19y+VdjE9abSw+zCL852gqCoZIQEgNJd3JCNgvDLQ3zM3PM5KbgSM8JCsjbafhjLpsmShje2oGI13UQHP7w3Ak/w7NY= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1729151064; c=relaxed/simple; bh=cnyVrXHUSLxpqT3tVAOcGrT5O5nt2KFsJZpwLWNWkWo=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=OxMKs4Ml1xZQV8N9XTMgSW/9LGl3uQOEUY7+EbkWajXZQ1VvM5r7oBeHi+GDS/zKq10DArMd3Efm36tws54EXGwgytppUq6vh/Ipg9MxC8ENN1unQR3WrlFifvCKoHs9vpiMBIHBtDXceOOeeGrsC3YVA4iNgM3/6t7iHBSHe00= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com; spf=pass smtp.mailfrom=arm.com; arc=none smtp.client-ip=217.140.110.172 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=arm.com Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 6602DFEC; Thu, 17 Oct 2024 00:44:52 -0700 (PDT) Received: from [10.57.66.61] (unknown [10.57.66.61]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id EACE83F528; Thu, 17 Oct 2024 00:44:15 -0700 (PDT) Message-ID: Date: Thu, 17 Oct 2024 09:44:13 +0200 Precedence: bulk X-Mailing-List: linux-kselftest@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v5 19/30] arm64: add POE signal support To: Joey Gouly , Will Deacon Cc: linux-arm-kernel@lists.infradead.org, nd@arm.com, akpm@linux-foundation.org, aneesh.kumar@kernel.org, aneesh.kumar@linux.ibm.com, anshuman.khandual@arm.com, bp@alien8.de, broonie@kernel.org, catalin.marinas@arm.com, christophe.leroy@csgroup.eu, dave.hansen@linux.intel.com, hpa@zytor.com, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, linuxppc-dev@lists.ozlabs.org, maz@kernel.org, mingo@redhat.com, mpe@ellerman.id.au, naveen.n.rao@linux.ibm.com, npiggin@gmail.com, oliver.upton@linux.dev, shuah@kernel.org, skhan@linuxfoundation.org, szabolcs.nagy@arm.com, tglx@linutronix.de, x86@kernel.org, kvmarm@lists.linux.dev, linux-kselftest@vger.kernel.org References: <20240822151113.1479789-1-joey.gouly@arm.com> <20240822151113.1479789-20-joey.gouly@arm.com> <47e1537f-5b60-4541-aed1-a20e804c137d@arm.com> <20241009144301.GA12453@willie-the-truck> <20241014171023.GA18295@willie-the-truck> <20241015095911.GA3777204@e124191.cambridge.arm.com> <20241015114116.GA19334@willie-the-truck> <20241015122529.GA3820764@e124191.cambridge.arm.com> Content-Language: en-GB From: Kevin Brodsky In-Reply-To: <20241015122529.GA3820764@e124191.cambridge.arm.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 15/10/2024 14:25, Joey Gouly wrote: > On Tue, Oct 15, 2024 at 12:41:16PM +0100, Will Deacon wrote: >> On Tue, Oct 15, 2024 at 10:59:11AM +0100, Joey Gouly wrote: >>> On Mon, Oct 14, 2024 at 06:10:23PM +0100, Will Deacon wrote: >>>> Kevin, Joey, >>>> >>>> On Wed, Oct 09, 2024 at 03:43:01PM +0100, Will Deacon wrote: >>>>> On Tue, Sep 24, 2024 at 01:27:58PM +0200, Kevin Brodsky wrote: >>>>>> On 22/08/2024 17:11, Joey Gouly wrote: >>>>>>> @@ -1178,6 +1237,9 @@ static void setup_return(struct pt_regs *regs, struct k_sigaction *ka, >>>>>>> sme_smstop(); >>>>>>> } >>>>>>> >>>>>>> + if (system_supports_poe()) >>>>>>> + write_sysreg_s(POR_EL0_INIT, SYS_POR_EL0); >>>>>> At the point where setup_return() is called, the signal frame has >>>>>> already been written to the user stack. In other words, we write to the >>>>>> user stack first, and then reset POR_EL0. This may be problematic, >>>>>> especially if we are using the alternate signal stack, which the >>>>>> interrupted POR_EL0 may not grant access to. In that situation uaccess >>>>>> will fail and we'll end up with a SIGSEGV. >>>>>> >>>>>> This issue has already been discussed on the x86 side, and as it happens >>>>>> patches to reset PKRU early [1] have just landed. I don't think this is >>>>>> a blocker for getting this series landed, but we should try and align >>>>>> with x86. If there's no objection, I'm planning to work on a counterpart >>>>>> to the x86 series (resetting POR_EL0 early during signal delivery). >>>>> Did you get a chance to work on that? It would be great to land the >>>>> fixes for 6.12, if possible, so that the first kernel release with POE >>>>> support doesn't land with known issues. >>>> Looking a little more at this, I think we have quite a weird behaviour >>>> on arm64 as it stands. It looks like we rely on the signal frame to hold >>>> the original POR_EL0 so, if for some reason we fail to allocate space >>>> for the POR context, I think we'll return back from the signal with >>>> POR_EL0_INIT. That seems bad? >>> If we don't allocate space for POR_EL0, I think the program recieves SIGSGEV? >>> >>> setup_sigframe_layout() >>> if (system_supports_poe()) { >>> err = sigframe_alloc(user, &user->poe_offset, >>> sizeof(struct poe_context)); >>> if (err) >>> return err; >>> } >>> >>> Through get_sigframe() and setup_rt_frame(), that eventually hets here: >>> >>> handle_signal() >>> ret = setup_rt_frame(usig, ksig, oldset, regs); >>> >>> [..] >>> >>> signal_setup_done(ret, ksig, test_thread_flag(TIF_SINGLESTEP)); >>> >>> void signal_setup_done(int failed, struct ksignal *ksig, int stepping) >>> { >>> if (failed) >>> force_sigsegv(ksig->sig); >>> else >>> signal_delivered(ksig, stepping); >>> } >>> >>> So I think it's "fine"? >> Ah, yes, sorry about that. I got confused by the conditional push in >> setup_sigframe(): >> >> if (system_supports_poe() && err == 0 && user->poe_offset) { >> ... >> >> which gives the wrong impression that the POR is somehow optional, even >> if the CPU supports POE. So we should drop that check of >> 'user->poe_offset' as it cannot be NULL here. >> >> We also still need to resolve Kevin's concern, which probably means >> keeping the thread's original POR around someplace. > That was cargo culted (by me) from the rest of the function (apart from TPIDR2 > and FPMR). I think Kevin is planning on sending his signal changes still, but > is on holiday, maybe he can remove the last part of the condition as part of > his series. Indeed just got back from holiday. I've got the series ready, about to send it. I will add a clean-up patch removing this check on poe_offset. Kevin