linux-kernel - Re: [PATCH v3 4/8] APEI: GHES: reserve a virtual page for SEI context

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Date:   Thu, 6 Apr 2017 17:25:32 +0800
From:   Xie XiuQi <xiexiuqi@...wei.com>
To:     James Morse <james.morse@....com>
CC:     <christoffer.dall@...aro.org>, <marc.zyngier@....com>,
        <catalin.marinas@....com>, <will.deacon@....com>,
        <fu.wei@...aro.org>, <rostedt@...dmis.org>,
        <hanjun.guo@...aro.org>, <shiju.jose@...wei.com>,
        <linux-arm-kernel@...ts.infradead.org>,
        <kvmarm@...ts.cs.columbia.edu>, <kvm@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, <linux-acpi@...r.kernel.org>,
        <gengdongjiu@...wei.com>, <zhengqiang10@...wei.com>,
        <wuquanming@...wei.com>, <wangxiongfeng2@...wei.com>
Subject: Re: [PATCH v3 4/8] APEI: GHES: reserve a virtual page for SEI context

Hi James,

Thanks for your comments.

On 2017/4/1 0:22, James Morse wrote:
> Hi Xie XiuQi,
> 
> On 30/03/17 11:31, Xie XiuQi wrote:
>> On arm64 platform, SEI may interrupt code which had interrupts masked.
>> But SEI could be masked, so it's not treated as NMI, however SEA is
>> treated as NMI.
>>
>> So, the  memory area used to transfer hardware error information from
>> BIOS to Linux can be determined only in NMI, SEI(arm64), IRQ or timer
>> handler.
>>
>> In this patch, we add a virtual page for SEI context.
> 
> I don't think this is the best way of solving the interaction problem. If we
> ever need to add another notification method this gets even more complicated,
> and the ioremap code has to know how these methods can interact.
> 
> 
>> diff --git a/drivers/acpi/apei/ghes.c b/drivers/acpi/apei/ghes.c
>> index 045d101..b1f9b1f 100644
>> --- a/drivers/acpi/apei/ghes.c
>> +++ b/drivers/acpi/apei/ghes.c
>> @@ -155,54 +162,55 @@ static void ghes_ioremap_exit(void)
> 
>> -static void __iomem *ghes_ioremap_pfn_irq(u64 pfn)
>> -{
>> -	unsigned long vaddr, paddr;
>> -	pgprot_t prot;
>> -
>> -	vaddr = (unsigned long)GHES_IOREMAP_IRQ_PAGE(ghes_ioremap_area->addr);
>> +	if (in_nmi()) {
>> +		raw_spin_lock(&ghes_ioremap_lock_nmi);
>> +		vaddr = (unsigned long)GHES_IOREMAP_NMI_PAGE(ghes_ioremap_area->addr);
>> +	} else if (this_cpu_read(sei_in_process)) {
> 
>> +		spin_lock_irqsave(&ghes_ioremap_lock_sei, flags);
> 
> I think this one should be a raw_spin_lock. I'm pretty sure this is for RT-linux
> where spin_lock() on a contented lock will call schedule() in the same way
> mutex_lock() does. If interrupts were masked by arch code then you need to use
> raw_spin_lock.
> So now we need to know how we got in here, we interrupted the SError handler so
> this should only be Synchronous External Abort. Having to know how we got here
> is another problem with this approach.
> 
> 
> As suggested earlier[0], I think the best way is to allocate one page of virtual
> address space per struct ghes, and move the locks out to the notify calls, which
> can know how they are called.
> 
> I've pushed a branch to:
> http://www.linux-arm.org/git?p=linux-jm.git;a=commit;h=refs/heads/apei_ioremap_rework/v1
> 

Good! I could rebase on your patch next time.

> I intend to post those patches as an RFC series later in the cycle, I've only
> build tested it so far.
> 
> 
> Thanks,
> 
> James
> 
>> +		vaddr = (unsigned long)GHES_IOREMAP_SEI_PAGE(ghes_ioremap_area->addr);
>> +	} else {
>> +		spin_lock_irqsave(&ghes_ioremap_lock_irq, flags);
>> +		vaddr = (unsigned long)GHES_IOREMAP_IRQ_PAGE(ghes_ioremap_area->addr);
>> +	}
> 
> 
> [0] https://lkml.org/lkml/2017/3/20/434
> 
> 
> .
> 

-- 
Thanks,
Xie XiuQi