From mboxrd@z Thu Jan 1 00:00:00 1970 From: Ingo Molnar Date: Tue, 19 Nov 2019 11:10:12 +0000 Subject: Re: [PATCH 00/12] treewide: break dependencies on x86's RM header Message-Id: <20191119111012.GA109842@gmail.com> List-Id: References: <20191119002121.4107-1-sean.j.christopherson@intel.com> In-Reply-To: <20191119002121.4107-1-sean.j.christopherson@intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: Sean Christopherson Cc: Thomas Gleixner , Ingo Molnar , Borislav Petkov , x86@kernel.org, "Rafael J. Wysocki" , Len Brown , Pavel Machek , Tony Luck , Fenghua Yu , Peter Zijlstra , Arnaldo Carvalho de Melo , Mark Rutland , Alexander Shishkin , Jiri Olsa , Namhyung Kim , "H. Peter Anvin" , Steven Rostedt , Ard Biesheuvel , Darren Hart , Andy Shevchenko , Nadav Amit , "VMware, Inc." , Arnd Bergmann , Greg Kroah-Hartman , Hans de Goede , Cezary Rojewski , Pierre-Louis Bossart , Liam Girdwood , Jie Yang , Mark Brown , Jaroslav Kysela , Takashi Iwai , linux-ia64@vger.kernel.org, linux-kernel@vger.kernel.org, linux-pm@vger.kernel.org, linux-efi@vger.kernel.org, platform-driver-x86@vger.kernel.org, linux-acpi@vger.kernel.org, alsa-devel@alsa-project.org * Sean Christopherson wrote: > x86's asm/realmode.h, which defines low level structures, variables and > helpers used to bring up APs during SMP boot, ends up getting included in > practically every nook and cranny of the kernel because the address used > by ACPI for resuming from S3 also happens to be stored in the real mode > header, and ACPI bleeds the dependency into its widely included headers. > > As a result, modifying realmode.h for even the most trivial change to the > boot code triggers a full kernel rebuild, which is frustrating to say the > least as it some of the most difficult code to get exactly right *and* is > also some of the most functionally isolated code in the kernel. > > To break the kernel's widespread dependency on realmode.h, add a wrapper > in the aforementioned ACPI S3 code to access the real mode header instead > of derefencing the header directly in asm/acpi.h and thereby exposing it > to the world via linux/acpi.h. > > Build tested on x86 with allyesconfig and allmodconfig, so hopefully there > aren't more build issues lurking, but at this point it wouldn't surprise > me in the least if this somehow manages to break the build. > > Based on tip/master, commit ceceaf1f12ba ("Merge branch 'WIP.x86/cleanups'"). > > Patch Synopsis: > - Patches 01-09 fix a variety of build errors that arise when patch 12 > drops realmode.h from asm/acpi.h. Most of the errors are quite absurb > as they have no relation whatsoever to x86's RM boot code, but occur > because realmode.h happens to include asm/io.h. Yeah, these kind of parasitic header dependencies are the main driving force behind kernel header spaghetti hell: it's super easy to add a new header, but very hard to remove them... Hence they practically only accumulate. As a result header removal patches get priority, from me at least. :-) > - Patch 10 removes a spurious include of realmode.h from an ACPI header. > > - Patches 11 and 12 implement the wrapper and move it out of acpi.h. So if the ACPI maintainers are fine with -tip carrying patches #11 and #12 then I'd be glad to route these patches upstream. I've applied them to tip:WIP.core/headers as a work-in-progress tree, and I'm testing them on randconfigs to make sure there's no broken dependencies. I'll wait for the ACPI acks. I edited the title of patch 12 slightly, to: c8bceb321209: x86/ACPI/sleep: Move acpi_wakeup_address() definition into sleep.c, remove from to make sure the big header dependency change is obvious at first sight. Thanks, Ingo