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Mon, 14 Oct 2024 17:10:26 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1728925831; bh=iLl0lXkXeALAMr5KDjF+8vkYFyZnHpji9UAQw4I8NLM=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=fZuGXBvfqai+/3NsOa9W9cD3IlOY9aT3U0WbINyOpuWErGCK6ZB6IOUBzMOrcOcny pu72RD2Q/eOijBUJKudsa5AgJol2pWXeoLojf4MNniYLbSJgH2kEtVhDGVb6Gm14Df 9EGatG41Z1BUkjfjmG1t0dtC3E9OVP/UsR4ZXtN7/cC9OYFti03Mmwc+YQYgMcx9FF id1TyF5286pt2Y3czQbj/ZxkcUQEN2KJW1lxao1NLV3WYoMqD/KKpW+g9w8uWA2Aqn /L7Px0nG8PKBofrF7r6MreT7d1B0i8Jz1iBY6w6RO2ZAzUeeOvYCehz+aQLkdHLfpI KopOxy2RDs1Dw== Date: Mon, 14 Oct 2024 18:10:23 +0100 From: Will Deacon To: Kevin Brodsky Cc: Joey Gouly , 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 Subject: Re: [PATCH v5 19/30] arm64: add POE signal support Message-ID: <20241014171023.GA18295@willie-the-truck> 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> X-Mailing-List: linuxppc-dev@lists.ozlabs.org List-Id: List-Help: List-Post: List-Subscribe: , , List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20241009144301.GA12453@willie-the-truck> User-Agent: Mutt/1.10.1 (2018-07-13) 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? Will