Date:   Fri, 28 Jul 2017 01:53:25 +0000
From:   "Zheng, Lv" <lv.zheng@...el.com>
To:     Dou Liyang <douly.fnst@...fujitsu.com>,
        "bhe@...hat.com" <bhe@...hat.com>
CC:     "x86@...nel.org" <x86@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "mingo@...nel.org" <mingo@...nel.org>,
        "hpa@...or.com" <hpa@...or.com>,
        "ebiederm@...ssion.com" <ebiederm@...ssion.com>,
        "peterz@...radead.org" <peterz@...radead.org>,
        "izumi.taku@...fujitsu.com" <izumi.taku@...fujitsu.com>,
        "tokunaga.keiich@...fujitsu.com" <tokunaga.keiich@...fujitsu.com>,
        "linux-acpi@...r.kernel.org" <linux-acpi@...r.kernel.org>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Julian Wollrath <jwollrath@....de>
Subject: RE: [PATCH v7 12/13] ACPI / init: Invoke early ACPI initialization
 earlier

Hi,

> From: Dou Liyang [mailto:douly.fnst@...fujitsu.com]
> Sent: Tuesday, July 18, 2017 5:44 PM
> Subject: Re: [PATCH v7 12/13] ACPI / init: Invoke early ACPI initialization earlier
> 
> Hi Baoquan,
> 
> At 07/18/2017 04:45 PM, bhe@...hat.com wrote:
> > On 07/18/17 at 02:08pm, Dou Liyang wrote:
> >> Hi, Zheng
> >>
> >> At 07/18/2017 01:18 PM, Zheng, Lv wrote:
> >>> Hi,
> >>>
> >>> Can the problem be fixed by invoking acpi_put_table() for mapped DMAR table?
> >>
> >> Invoking acpi_put_table() is my first choice. But it made the kernel
> >> *panic* when we try to get the table again in intel_iommu_init() in
> >> late stage.
> >>
> >> I am also confused that:
> >>
> >> There are two places where we used DMAR table in Linux:
> >>
> >> 1) In detect_intel_iommu() in ACPI early stage:
> >>
> >> ...
> >> status = acpi_get_table(ACPI_SIG_DMAR, 0, &dmar_tbl);
> >> ....
> >> if (dmar_tbl) {
> >> 	acpi_put_table(dmar_tbl);
> >> 	dmar_tbl = NULL;
> >> }
> >>
> >> 2) In dmar_table_init() in ACPI late stage:
> >>
> >> ...
> >> status = acpi_get_table(ACPI_SIG_DMAR, 0, &dmar_tbl);
> >> ...
> >>
> >> As we know, dmar_table_init() is called by intel_iommu_init() and
> >> intel_prepare_irq_remapping().
> >>
> >> When I invoked acpi_put_table() in the intel_prepare_irq_remapping() in
> >> early stage like 1) shows, kernel will panic.
> >
> > That's because acpi_put_table() will make the table pointer be NULL,
> > while dmar_table_init() will skip parse_dmar_table() calling if
> > dmar_table_initialized is set to 1 in intel_prepare_irq_remapping().
> >
> 
> Correctly.
> 
> I have considered and removed the *dmar_table_initialized* in this
> situation. So, dmar_table_init() didn't skip parse_dmar_table()
> calling.
> 
> I didn't dig into the cause, I think it is interesting, I will do it
> right now and share with you later.
> 
> > Dmar hardware support interrupt remapping and io remapping separately. But
> > intel_iommu_init() is called later than intel_prepare_irq_remapping().
> > So what if make dmar_table_init() a reentrant function? You can just
> > have a try, but maybe not a good idea, the dmar table will be parsed
> > twice.
> 
> Yes, It is precisely one reason that I gave up invoking
> acpi_put_table().

Parsing a table twice is not a problem on x86.
If you check the code, there are many examples.
It's actually required if you want to use a table both in early stage and late stage.

Thanks

> 
> Thanks,
> 
> 	dou.
> 
> >
> >>
> >>
> >> Thanks,
> >>
> >> 	dou.
> >>>
> >>> Thanks
> >>> Lv
> >>>
> >>>> From: Dou Liyang [mailto:douly.fnst@...fujitsu.com]
> >>>> Sent: Friday, July 14, 2017 1:53 PM
> >>>> To: x86@...nel.org; linux-kernel@...r.kernel.org
> >>>> Cc: tglx@...utronix.de; mingo@...nel.org; hpa@...or.com; ebiederm@...ssion.com; bhe@...hat.com;
> >>>> peterz@...radead.org; izumi.taku@...fujitsu.com; tokunaga.keiich@...fujitsu.com; Dou Liyang
> >>>> <douly.fnst@...fujitsu.com>; linux-acpi@...r.kernel.org; Rafael J. Wysocki <rjw@...ysocki.net>;
> Zheng,
> >>>> Lv <lv.zheng@...el.com>; Julian Wollrath <jwollrath@....de>
> >>>> Subject: [PATCH v7 12/13] ACPI / init: Invoke early ACPI initialization earlier
> >>>>
> >>>> Linux uses acpi_early_init() to put the ACPI table management into
> >>>> the late stage from the early stage where the mapped ACPI tables is
> >>>> temporary and should be unmapped.
> >>>>
> >>>> But, now initializing interrupt delivery mode should map and parse the
> >>>> DMAR table earlier in the early stage. This causes an ACPI error when
> >>>> Linux reallocates the ACPI root tables. Because Linux doesn't unmapped
> >>>> the DMAR table after using in the early stage.
> >>>>
> >>>> Invoke acpi_early_init() earlier before late_time_init(), Keep the DMAR
> >>>> be mapped and parsed in late stage like before.
> >>>>
> >>>> Reported-by: Xiaolong Ye <xiaolong.ye@...el.com>
> >>>> Signed-off-by: Dou Liyang <douly.fnst@...fujitsu.com>
> >>>> Cc: linux-acpi@...r.kernel.org
> >>>> Cc: Rafael J. Wysocki <rjw@...ysocki.net>
> >>>> Cc: Zheng, Lv <lv.zheng@...el.com>
> >>>> Cc: Julian Wollrath <jwollrath@....de>
> >>>> ---
> >>>> Test in my own PC(Lenovo M4340).
> >>>> Ask help for doing regression testing for the bug said in commit c4e1acbb35e4
> >>>> ("ACPI / init: Invoke early ACPI initialization later").
> >>>>
> >>>>  init/main.c | 2 +-
> >>>>  1 file changed, 1 insertion(+), 1 deletion(-)
> >>>>
> >>>> diff --git a/init/main.c b/init/main.c
> >>>> index df58a41..7a09467 100644
> >>>> --- a/init/main.c
> >>>> +++ b/init/main.c
> >>>> @@ -654,12 +654,12 @@ asmlinkage __visible void __init start_kernel(void)
> >>>>  	kmemleak_init();
> >>>>  	setup_per_cpu_pageset();
> >>>>  	numa_policy_init();
> >>>> +	acpi_early_init();
> >>>>  	if (late_time_init)
> >>>>  		late_time_init();
> >>>>  	calibrate_delay();
> >>>>  	pidmap_init();
> >>>>  	anon_vma_init();
> >>>> -	acpi_early_init();
> >>>>  #ifdef CONFIG_X86
> >>>>  	if (efi_enabled(EFI_RUNTIME_SERVICES))
> >>>>  		efi_enter_virtual_mode();
> >>>> --
> >>>> 2.5.5
> >>>>
> >>>>
> >>>
> >>>
> >>>
> >>>
> >>
> >>
> >
> >
> >
> 

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