From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-10.3 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,NICE_REPLY_A, SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 7A27CC433E0 for ; Tue, 23 Mar 2021 11:41:00 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 48B4E619BA for ; Tue, 23 Mar 2021 11:41:00 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229900AbhCWLk3 (ORCPT ); Tue, 23 Mar 2021 07:40:29 -0400 Received: from foss.arm.com ([217.140.110.172]:44456 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230114AbhCWLkI (ORCPT ); Tue, 23 Mar 2021 07:40:08 -0400 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 963B01042; Tue, 23 Mar 2021 04:40:07 -0700 (PDT) Received: from [192.168.0.110] (unknown [172.31.20.19]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 1BC843F719; Tue, 23 Mar 2021 04:40:06 -0700 (PDT) Subject: Re: [kvm-unit-tests PATCH 0/4] RFC: Minor arm/arm64 MMU fixes and checks To: Andrew Jones , Nikos Nikoleris Cc: kvm@vger.kernel.org References: <20210319122414.129364-1-nikos.nikoleris@arm.com> <20210323112411.6uwqex6x2py4va6d@kamzik.brq.redhat.com> From: Alexandru Elisei Message-ID: <0f27d865-e16d-e933-4dfa-a3661437c5d2@arm.com> Date: Tue, 23 Mar 2021 11:40:37 +0000 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.8.1 MIME-Version: 1.0 In-Reply-To: <20210323112411.6uwqex6x2py4va6d@kamzik.brq.redhat.com> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Content-Language: en-US Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org Hi Drew, On 3/23/21 11:24 AM, Andrew Jones wrote: > On Fri, Mar 19, 2021 at 12:24:10PM +0000, Nikos Nikoleris wrote: >> Prior to this set of fixes, the code in setup() which we call to >> initialize the system has a circular dependency. cpu_init() >> (eventually) calls spin_lock() and __mmu_enabled(). However, at this >> point, __mmu_enabled() may have undefined behavior as we haven't >> initialized the current thread_info (cpu field). Moving >> thread_info_init() above cpu_init() is not possible as it relies on >> mpidr_to_cpu() which won't return the right results before cpu_init(). >> In addition, mem_init() also calls __mmu_enabled() and therefore >> suffers from the same problem. Right now, everything works as >> thread_info maps to memory which is implicitly initialized to 0 (cpu = >> 0) and makes the assumption that the cpu that runs setup() will be the >> first cpu in the DT. >> >> This set of patches changes the code slightly and avoids this >> assumptions. In addition, it adds assertions to catch problems like >> the above. The current solution relies on the thread_info() of the cpu >> that setup() run to be initialized to zero (should we make it >> explicit?). >> >> There are a couple of options I considered in addressing this issue >> which didn't seem satisfactory: >> >> - Change the mmu_disabled_count global variable to mmu_enabled_count >> to count the number of active mmu's and bypass __mmu_enabled() when >> it's 0. This is a global variable and at the momement all write to >> it are protected by a lock but it's rather fragile and could easily >> cause issues in the future. >> - Explicitly initialize current_thread_info()->cpu = 0 in setup() >> before anything else or make the first call of thread_info_init() a >> special case and avoid looking up mpidr_to_cpu(). This way we can >> move thread_info_init() to the top of setup(). If the CPU setup is >> running on is not the first that appears in the DT then this >> solution won't work. >> >> Thanks, >> >> Nikos >> >> Nikos Nikoleris (4): >> arm/arm64: Avoid calling cpumask_test_cpu for CPUs above nr_cpu >> arm/arm64: Read system registers to get the state of the MMU >> arm/arm64: Track whether thread_info has been initialized >> arm/arm64: Add sanity checks to the cpumask API >> >> lib/arm/asm/cpumask.h | 7 ++++++- >> lib/arm/asm/mmu-api.h | 7 +------ >> lib/arm/asm/processor.h | 7 +++++++ >> lib/arm/asm/thread_info.h | 1 + >> lib/arm64/asm/processor.h | 1 + >> lib/arm/mmu.c | 16 ++++++++-------- >> lib/arm/processor.c | 10 ++++++++-- >> lib/arm64/processor.c | 10 ++++++++-- >> 8 files changed, 40 insertions(+), 19 deletions(-) >> >> -- >> 2.25.1 >> > Hi Nikos, > > So, I like patches 1, 2, and 4. I think 3 can be dropped with the > addition of "arm/arm64: Zero BSS and stack at startup". Would you > agree? I've applied all the updated commit messages and all of > Alexandru's suggestions to 2. Patch 2 now looks like the diff below. > > Alexandru, are you satisfied with 1, 2, and 4? If so, please let me > know and I'll add r-b's for you before queuing. The diff looks good, and I agree that we can come back to #3 once we have a better understanding of what needs to be done. Patch #1 is a nice fix for what I imagine was a hard to find bug. Patch #4 also looks correct to me. Yes, please add my Reviewed-by for the series. Thanks, Alex > > Thanks, > drew > > > diff --git a/lib/arm/asm/mmu-api.h b/lib/arm/asm/mmu-api.h > index 3d04d0312622..05fc12b5afb8 100644 > --- a/lib/arm/asm/mmu-api.h > +++ b/lib/arm/asm/mmu-api.h > @@ -5,12 +5,7 @@ > #include > > extern pgd_t *mmu_idmap; > -extern unsigned int mmu_disabled_cpu_count; > -extern bool __mmu_enabled(void); > -static inline bool mmu_enabled(void) > -{ > - return mmu_disabled_cpu_count == 0 || __mmu_enabled(); > -} > +extern bool mmu_enabled(void); > extern void mmu_mark_enabled(int cpu); > extern void mmu_mark_disabled(int cpu); > extern void mmu_enable(pgd_t *pgtable); > diff --git a/lib/arm/asm/processor.h b/lib/arm/asm/processor.h > index 273366d1fe1c..6b762ad060eb 100644 > --- a/lib/arm/asm/processor.h > +++ b/lib/arm/asm/processor.h > @@ -67,11 +67,13 @@ extern int mpidr_to_cpu(uint64_t mpidr); > ((mpidr >> MPIDR_LEVEL_SHIFT(level)) & 0xff) > > extern void start_usr(void (*func)(void *arg), void *arg, unsigned long sp_usr); > +extern bool __mmu_enabled(void); > extern bool is_user(void); > > #define CNTVCT __ACCESS_CP15_64(1, c14) > #define CNTFRQ __ACCESS_CP15(c14, 0, c0, 0) > #define CTR __ACCESS_CP15(c0, 0, c0, 1) > +#define SCTRL __ACCESS_CP15(c1, 0, c0, 0) > > static inline u64 get_cntvct(void) > { > diff --git a/lib/arm/mmu.c b/lib/arm/mmu.c > index a1862a55db8b..15eef007f256 100644 > --- a/lib/arm/mmu.c > +++ b/lib/arm/mmu.c > @@ -24,13 +24,10 @@ extern unsigned long etext; > pgd_t *mmu_idmap; > > /* CPU 0 starts with disabled MMU */ > -static cpumask_t mmu_disabled_cpumask = { {1} }; > -unsigned int mmu_disabled_cpu_count = 1; > +static cpumask_t mmu_enabled_cpumask; > > -bool __mmu_enabled(void) > +bool mmu_enabled(void) > { > - int cpu = current_thread_info()->cpu; > - > /* > * mmu_enabled is called from places that are guarding the > * use of exclusive ops (which require the mmu to be enabled). > @@ -38,19 +35,22 @@ bool __mmu_enabled(void) > * spinlock, atomic bitop, etc., otherwise we'll recurse. > * [cpumask_]test_bit is safe though. > */ > - return !cpumask_test_cpu(cpu, &mmu_disabled_cpumask); > + if (is_user()) { > + int cpu = current_thread_info()->cpu; > + return cpumask_test_cpu(cpu, &mmu_enabled_cpumask); > + } > + > + return __mmu_enabled(); > } > > void mmu_mark_enabled(int cpu) > { > - if (cpumask_test_and_clear_cpu(cpu, &mmu_disabled_cpumask)) > - --mmu_disabled_cpu_count; > + cpumask_set_cpu(cpu, &mmu_enabled_cpumask); > } > > void mmu_mark_disabled(int cpu) > { > - if (!cpumask_test_and_set_cpu(cpu, &mmu_disabled_cpumask)) > - ++mmu_disabled_cpu_count; > + cpumask_clear_cpu(cpu, &mmu_enabled_cpumask); > } > > extern void asm_mmu_enable(phys_addr_t pgtable); > diff --git a/lib/arm/processor.c b/lib/arm/processor.c > index 773337e6d3b7..9d5759686b73 100644 > --- a/lib/arm/processor.c > +++ b/lib/arm/processor.c > @@ -145,3 +145,8 @@ bool is_user(void) > { > return current_thread_info()->flags & TIF_USER_MODE; > } > + > +bool __mmu_enabled(void) > +{ > + return read_sysreg(SCTRL) & CR_M; > +} > diff --git a/lib/arm64/asm/processor.h b/lib/arm64/asm/processor.h > index 771b2d1e0c94..8e2037e1a43e 100644 > --- a/lib/arm64/asm/processor.h > +++ b/lib/arm64/asm/processor.h > @@ -98,6 +98,7 @@ extern int mpidr_to_cpu(uint64_t mpidr); > > extern void start_usr(void (*func)(void *arg), void *arg, unsigned long sp_usr); > extern bool is_user(void); > +extern bool __mmu_enabled(void); > > static inline u64 get_cntvct(void) > { > diff --git a/lib/arm64/processor.c b/lib/arm64/processor.c > index 2a024e3f4e9d..ef558625e284 100644 > --- a/lib/arm64/processor.c > +++ b/lib/arm64/processor.c > @@ -257,3 +257,8 @@ bool is_user(void) > { > return current_thread_info()->flags & TIF_USER_MODE; > } > + > +bool __mmu_enabled(void) > +{ > + return read_sysreg(sctlr_el1) & SCTLR_EL1_M; > +} >