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=-15.3 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, MENTIONS_GIT_HOSTING,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 9E75EC433DB for ; Tue, 23 Mar 2021 12:16:02 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 5E075619B3 for ; Tue, 23 Mar 2021 12:16:02 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230097AbhCWMPb (ORCPT ); Tue, 23 Mar 2021 08:15:31 -0400 Received: from foss.arm.com ([217.140.110.172]:45538 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230252AbhCWMPP (ORCPT ); Tue, 23 Mar 2021 08:15:15 -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 487C1D6E; Tue, 23 Mar 2021 05:15:15 -0700 (PDT) Received: from C02W217MHV2R.local (unknown [10.57.24.109]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id B145A3F719; Tue, 23 Mar 2021 05:15:14 -0700 (PDT) Subject: Re: [kvm-unit-tests PATCH 0/4] RFC: Minor arm/arm64 MMU fixes and checks To: Andrew Jones , Alexandru Elisei Cc: kvm@vger.kernel.org References: <20210319122414.129364-1-nikos.nikoleris@arm.com> <20210323112411.6uwqex6x2py4va6d@kamzik.brq.redhat.com> <0f27d865-e16d-e933-4dfa-a3661437c5d2@arm.com> <20210323115156.axp2frk73byimz4o@kamzik.brq.redhat.com> From: Nikos Nikoleris Message-ID: <7596f395-7e20-72bc-bb21-8d1ffb745ca8@arm.com> Date: Tue, 23 Mar 2021 12:15:13 +0000 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.16; rv:78.0) Gecko/20100101 Thunderbird/78.8.1 MIME-Version: 1.0 In-Reply-To: <20210323115156.axp2frk73byimz4o@kamzik.brq.redhat.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org On 23/03/2021 11:51, Andrew Jones wrote: > On Tue, Mar 23, 2021 at 11:40:37AM +0000, Alexandru Elisei wrote: >> 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, applied 1, 2, and 4 to arm/queue > > https://gitlab.com/rhdrjones/kvm-unit-tests/-/commits/arm/queue > > Thanks, > drew > Looks good to me. Thank you both for the reviews and the suggestions! Thanks, Nikos > >> >>> >>> 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; >>> +} >>> >> >