From mboxrd@z Thu Jan 1 00:00:00 1970 From: James Morse Subject: Re: [PATCH v7 20/25] ACPI / APEI: Use separate fixmap pages for arm64 NMI-like notifications Date: Wed, 23 Jan 2019 18:33:02 +0000 Message-ID: References: <20181203180613.228133-1-james.morse@arm.com> <20181203180613.228133-21-james.morse@arm.com> <20190121172743.GN29166@zn.tnic> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20190121172743.GN29166@zn.tnic> Content-Language: en-GB List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: kvmarm-bounces@lists.cs.columbia.edu Sender: kvmarm-bounces@lists.cs.columbia.edu To: Borislav Petkov Cc: Rafael Wysocki , Tony Luck , Fan Wu , linux-mm@kvack.org, Marc Zyngier , Catalin Marinas , Will Deacon , Dongjiu Geng , linux-acpi@vger.kernel.org, Naoya Horiguchi , kvmarm@lists.cs.columbia.edu, linux-arm-kernel@lists.infradead.org, Len Brown List-Id: linux-acpi@vger.kernel.org Hi Boris, On 21/01/2019 17:27, Borislav Petkov wrote: > On Mon, Dec 03, 2018 at 06:06:08PM +0000, James Morse wrote: >> Now that ghes notification helpers provide the fixmap slots and >> take the lock themselves, multiple NMI-like notifications can >> be used on arm64. >> >> These should be named after their notification method as they can't >> all be called 'NMI'. x86's NOTIFY_NMI already is, change the SEA >> fixmap entry to be called FIX_APEI_GHES_SEA. >> >> Future patches can add support for FIX_APEI_GHES_SEI and >> FIX_APEI_GHES_SDEI_{NORMAL,CRITICAL}. >> >> Because all of ghes.c builds on both architectures, provide a >> constant for each fixmap entry that the architecture will never >> use. >> diff --git a/drivers/acpi/apei/ghes.c b/drivers/acpi/apei/ghes.c >> index 849da0d43a21..6cbf9471b2a2 100644 >> --- a/drivers/acpi/apei/ghes.c >> +++ b/drivers/acpi/apei/ghes.c >> @@ -85,6 +85,14 @@ >> ((struct acpi_hest_generic_status *) \ >> ((struct ghes_estatus_node *)(estatus_node) + 1)) >> >> +/* NMI-like notifications vary by architecture. Fill in the fixmap gaps */ >> +#ifndef CONFIG_HAVE_ACPI_APEI_NMI >> +#define FIX_APEI_GHES_NMI -1 >> +#endif >> +#ifndef CONFIG_ACPI_APEI_SEA >> +#define FIX_APEI_GHES_SEA -1 > > I'm guessing those -1 are going to cause __set_fixmap() to fail, right? It shouldn't be possible, these are just to give the compiler something int shaped to work with, until it prunes all the callers. But for arm64, yes if would fail. -1 shouldn't alias an existing entry, and it will get caught by: | BUG_ON(idx <= FIX_HOLE || idx >= __end_of_fixed_addresses); I wanted BUILD_BUG_ON() here, as any user of these should be optimised out, but the compiler choked on that. __end_of_fixed_addresses would be a better arch-agnostic invalid value. It has to be defined as the last value in the enum for core code's fix_to_virt() to work. These two look like something left behind from when we had different #ifdeffery. The users of these two are now behind arch specific #ifdefs that since patch 12 of this series, can't be turned off, so I can remove these. We do need them for SDEI, as it is relying on IS_ENABLED() and the compiler's dead code elimination. But the compiler wants that symbol to have the right type before it gets that far. |#define FIX_APEI_GHES_SDEI_NORMAL (BUILD_BUG(), -1) Was the best I had, but this trips the BUILD_BUG() too early. With it, x86 BUILD_BUG()s. With just the -1 the path gets pruned out, and there are no 'sdei' symbols in the object file. ...at this point, I stopped caring! > I'm wondering if we could catch that situation in ghes_map() already to > protect ourselves against future changes in the fixmap code... We already skip registering notifiers if the kconfig option wasn't selected. We can't catch this at compile time, as the dead-code elimination seems to happen in multiple passes. I'll switch the SDEI ones to __end_of_fixed_addresses, as both architectures BUG() when they see this. Thanks, James