From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751224Ab1HJNLn (ORCPT ); Wed, 10 Aug 2011 09:11:43 -0400 Received: from nat28.tlf.novell.com ([130.57.49.28]:21202 "EHLO nat28.tlf.novell.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750779Ab1HJNLl convert rfc822-to-8bit (ORCPT ); Wed, 10 Aug 2011 09:11:41 -0400 Message-Id: <4E429FE30200007800050910@nat28.tlf.novell.com> X-Mailer: Novell GroupWise Internet Agent 8.0.1 Date: Wed, 10 Aug 2011 14:12:35 +0100 From: "Jan Beulich" To: "Ingo Molnar" Cc: "Jeremy Fitzhardinge" , "Matt Fleming" , "Thomas Gleixner" , , "Avi Kivity" , , "Marcelo Tosatti" , "johnstultz" , Subject: Re: [PATCH] x86, efi: Don't recursively acquire rtc_lock References: <4E3C30C602000078000740D5@nat28.tlf.novell.com> <1312810836.10579.127.camel@mfleming-mobl1.ger.corp.intel.com> <4E4009A50200007800050258@nat28.tlf.novell.com> <20110810090330.GF26762@elte.hu> <4E426D4702000078000508B5@nat28.tlf.novell.com> <20110810095140.GB21059@elte.hu> In-Reply-To: <20110810095140.GB21059@elte.hu> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 8BIT Content-Disposition: inline Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org >>> On 10.08.11 at 11:51, Ingo Molnar wrote: > * Jan Beulich wrote: > >> >>> On 10.08.11 at 11:03, Ingo Molnar wrote: >> >> > * Jan Beulich wrote: >> > >> >> >>> On 08.08.11 at 15:40, Matt Fleming wrote: >> >> > On Fri, 2011-08-05 at 18:04 +0100, Jan Beulich wrote: >> >> >> >> >> >> Virtual platforms will have to take care of the serialization in the >> >> >> host anyway, so the guest side implementation of getwallclock et al >> >> >> is entirely unaffected. >> >> > >> >> > Ah, OK, that's the important part. I didn't realise that rtc_lock isn't >> >> > actually required by any other code. In which case, yes, it completely >> >> > makes sense to push the locking of rtc_lock down into the >> >> > implementations that actually need it. >> >> > >> >> > It'd be great if I could get some ACK's from the virtualization guys. >> >> > >> >> > --------8<-------- >> >> > >> >> > From a0a39dbb69f6ac675846bf00f30ad153506a4567 Mon Sep 17 00:00:00 2001 >> >> > From: Matt Fleming >> >> > Date: Mon, 8 Aug 2011 12:59:35 +0100 >> >> > Subject: [PATCH] x86, efi: Don't recursively acquire rtc_lock >> >> > >> >> > A deadlock was introduced on x86 in commit ef68c8f87ed1 ("x86: >> >> > Serialize EFI time accesses on rtc_lock") because efi_get_time() and >> >> > friends can be called with rtc_lock already held by >> >> > read_persistent_time(), e.g. >> >> > >> >> > timekeeping_init() >> >> > read_persistent_clock() <-- acquire rtc_lock >> >> > efi_get_time() >> >> > phys_efi_get_time() <-- acquire rtc_lock >> >> > >> >> > To fix this let's push the locking down into the get_wallclock() and >> >> > set_wallclock() implementations. Only the clock implementations that >> >> > access the x86 RTC directly need to acquire rtc_lock, so it makes >> >> > sense to push the locking down into the rtc, vrtc and efi code. >> >> > >> >> > The virtualization implementations don't require rtc_lock to be held >> >> > because they provide their own serialization. >> >> > >> >> > Signed-off-by: Matt Fleming >> >> >> >> Acked-by: Jan Beulich >> > >> > How urgent is thix fix - can it wait until Thomas comes back and >> > starts processing patches again? >> >> Without it booting on EFI can't be expected to work (and while I >> was really sure I tested this before submitting, I apparently must >> have used a stale kernel then - I'm really sorry for that), so >> getting it applied soon would be rather desirable. >> >> But then again I don't seem to be able to boot 3.0.1 with both >> patches applied on my only EFI box, so there must be something else >> that broke, and hence maybe I really did test it (on 3.0-rc7) and >> it worked then. Debugging... > > Ok, once you figure it out we can merge all fixes upstream ASAP. So this is a combination of two recent events: In my patch set, I recently removed efi.c's X86_32 conditional around setting x86_platform.[gs]et_wallclock. Without that removal, the deadlock wouldn't occur (because mach_get_cmos_time() would get called instead) on 64-bits, which is the only thing I run. With that conditional removed, Matthew's NX consolidation patch gets into the way: For the physical call path it is simply wrong (correct only for the phys_efi_set_virtual_address_map() call, as there the memory map got virtual addresses assigned already) - it switches from early_runtime_code_mapping_set_exec()'s using of md->phys_addr to efi_set_executable() using md->virt_addr. But the latter isn't set at that point yet. And it's unclear to me why this works on 32-bit. Bottom line - the fix here is needed for 32-bit booting only (and hence isn't - afaic - as critical as I first thought). But the adjustment I'm holding is a necessary one (and I don't even understand why, when 32- and 64-bit EFI code got merged, this was left 32-bit only), and the NX consolidation change needs to be fixed too (basically as a prerequisite). Jan