From: Juergen Gross <jgross@suse.com>
To: Will Deacon <will@kernel.org>, Elliot Berman <quic_eberman@quicinc.com>
Cc: "Srivatsa S. Bhat (VMware)" <srivatsa@csail.mit.edu>,
Alexey Makhalov <amakhalov@vmware.com>,
Catalin Marinas <catalin.marinas@arm.com>,
Prakruthi Deepak Heragu <quic_pheragu@quicinc.com>,
virtualization@lists.linux-foundation.org, x86@kernel.org,
linux-arm-kernel@lists.infradead.org,
linux-kernel@vger.kernel.org,
Murali Nalajala <quic_mnalajal@quicinc.com>,
stable@vger.kernel.org
Subject: Re: [PATCH v2] arm64: paravirt: Use RCU read locks to guard stolen_time
Date: Wed, 4 May 2022 15:38:47 +0200 [thread overview]
Message-ID: <c6689e42-e87c-0c0b-c7ff-40134406e080@suse.com> (raw)
In-Reply-To: <20220504094507.GA20305@willie-the-truck>
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On 04.05.22 11:45, Will Deacon wrote:
> On Thu, Apr 28, 2022 at 11:35:36AM -0700, Elliot Berman wrote:
>> From: Prakruthi Deepak Heragu <quic_pheragu@quicinc.com>
>>
>> During hotplug, the stolen time data structure is unmapped and memset.
>> There is a possibility of the timer IRQ being triggered before memset
>> and stolen time is getting updated as part of this timer IRQ handler. This
>> causes the below crash in timer handler -
>>
>> [ 3457.473139][ C5] Unable to handle kernel paging request at virtual address ffffffc03df05148
>> ...
>> [ 3458.154398][ C5] Call trace:
>> [ 3458.157648][ C5] para_steal_clock+0x30/0x50
>> [ 3458.162319][ C5] irqtime_account_process_tick+0x30/0x194
>> [ 3458.168148][ C5] account_process_tick+0x3c/0x280
>> [ 3458.173274][ C5] update_process_times+0x5c/0xf4
>> [ 3458.178311][ C5] tick_sched_timer+0x180/0x384
>> [ 3458.183164][ C5] __run_hrtimer+0x160/0x57c
>> [ 3458.187744][ C5] hrtimer_interrupt+0x258/0x684
>> [ 3458.192698][ C5] arch_timer_handler_virt+0x5c/0xa0
>> [ 3458.198002][ C5] handle_percpu_devid_irq+0xdc/0x414
>> [ 3458.203385][ C5] handle_domain_irq+0xa8/0x168
>> [ 3458.208241][ C5] gic_handle_irq.34493+0x54/0x244
>> [ 3458.213359][ C5] call_on_irq_stack+0x40/0x70
>> [ 3458.218125][ C5] do_interrupt_handler+0x60/0x9c
>> [ 3458.223156][ C5] el1_interrupt+0x34/0x64
>> [ 3458.227560][ C5] el1h_64_irq_handler+0x1c/0x2c
>> [ 3458.232503][ C5] el1h_64_irq+0x7c/0x80
>> [ 3458.236736][ C5] free_vmap_area_noflush+0x108/0x39c
>> [ 3458.242126][ C5] remove_vm_area+0xbc/0x118
>> [ 3458.246714][ C5] vm_remove_mappings+0x48/0x2a4
>> [ 3458.251656][ C5] __vunmap+0x154/0x278
>> [ 3458.255796][ C5] stolen_time_cpu_down_prepare+0xc0/0xd8
>> [ 3458.261542][ C5] cpuhp_invoke_callback+0x248/0xc34
>> [ 3458.266842][ C5] cpuhp_thread_fun+0x1c4/0x248
>> [ 3458.271696][ C5] smpboot_thread_fn+0x1b0/0x400
>> [ 3458.276638][ C5] kthread+0x17c/0x1e0
>> [ 3458.280691][ C5] ret_from_fork+0x10/0x20
>>
>> As a fix, introduce rcu lock to update stolen time structure.
>>
>> Fixes: 75df529bec91 ("arm64: paravirt: Initialize steal time when cpu is online")
>> Cc: stable@vger.kernel.org
>> Signed-off-by: Prakruthi Deepak Heragu <quic_pheragu@quicinc.com>
>> Signed-off-by: Elliot Berman <quic_eberman@quicinc.com>
>> ---
>> Changes since v1: https://lore.kernel.org/all/20220420204417.155194-1-quic_eberman@quicinc.com/
>> - Use RCU instead of disabling interrupts
>>
>> arch/arm64/kernel/paravirt.c | 24 +++++++++++++++++++-----
>> 1 file changed, 19 insertions(+), 5 deletions(-)
>>
>> diff --git a/arch/arm64/kernel/paravirt.c b/arch/arm64/kernel/paravirt.c
>> index 75fed4460407..e724ea3d86f0 100644
>> --- a/arch/arm64/kernel/paravirt.c
>> +++ b/arch/arm64/kernel/paravirt.c
>> @@ -52,7 +52,9 @@ early_param("no-steal-acc", parse_no_stealacc);
>> /* return stolen time in ns by asking the hypervisor */
>> static u64 para_steal_clock(int cpu)
>> {
>> + struct pvclock_vcpu_stolen_time *kaddr = NULL;
>> struct pv_time_stolen_time_region *reg;
>> + u64 ret = 0;
>>
>> reg = per_cpu_ptr(&stolen_time_region, cpu);
>>
>> @@ -61,28 +63,38 @@ static u64 para_steal_clock(int cpu)
>> * online notification callback runs. Until the callback
>> * has run we just return zero.
>> */
>> - if (!reg->kaddr)
>> + rcu_read_lock();
>> + kaddr = rcu_dereference(reg->kaddr);
>> + if (!kaddr) {
>> + rcu_read_unlock();
>> return 0;
>> + }
>>
>> - return le64_to_cpu(READ_ONCE(reg->kaddr->stolen_time));
>> + ret = le64_to_cpu(READ_ONCE(kaddr->stolen_time));
>
> Is this READ_ONCE() still required now?
Yes, as it might be called for another cpu than the current one.
stolen_time might just be updated, so you want to avoid load tearing.
Juergen
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next prev parent reply other threads:[~2022-05-04 13:38 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-04-28 18:35 [PATCH v2] arm64: paravirt: Use RCU read locks to guard stolen_time Elliot Berman
2022-05-04 9:45 ` Will Deacon
2022-05-04 13:38 ` Juergen Gross [this message]
2022-05-04 13:50 ` Will Deacon
2022-05-04 13:40 ` Juergen Gross
2022-05-05 10:49 ` Will Deacon
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