Message-ID: <7716ac99-34a1-2364-03ee-6ecd92b39f5b@linux.alibaba.com>
Date:   Thu, 21 Oct 2021 23:46:40 +0800
From:   Xuesong Chen <xuesong.chen@...ux.alibaba.com>
To:     Bjorn Helgaas <helgaas@...nel.org>
Cc:     catalin.marinas@....com, lorenzo.pieralisi@....com,
        james.morse@....com, will@...nel.org, rafael@...nel.org,
        tony.luck@...el.com, bp@...en8.de, mingo@...nel.org,
        bhelgaas@...gle.com, linux-pci@...r.kernel.org,
        linux-acpi@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org, Huang Ying <ying.huang@...el.com>,
        Gong <gong.chen@...ux.intel.com>, xuesong.chen@...ux.alibaba.com
Subject: Re: [PATCH v3 2/2] ACPI: APEI: Filter the PCI MCFG address with an
 arch-agnostic method



On 21/10/2021 02:50, Bjorn Helgaas wrote:
> [+cc Gong, author of d91525eb8ee6]
> 
> On Wed, Oct 20, 2021 at 11:16:38AM +0800, Xuesong Chen wrote:
>> On 20/10/2021 03:23, Bjorn Helgaas wrote:
>>> On Tue, Oct 19, 2021 at 12:50:33PM +0800, Xuesong Chen wrote:
> 
>>> I wish we could also include the matching MCFG info For x86, we
>>> put something like this in the dmesg log, but I guess pci_mcfg.c
>>> doesn't do this:
>>>
>>>   PCI: MMCONFIG for domain 0000 [bus 00-7f] at [mem 0xf0000000-0xf7ffffff] (base 0xf0000000)
>>
>> I can add the similar dmesg log in pci_mcfg.c to make it's
>> consistent between different arches
> 
> I think that might be nice.  It should probably be a separate patch
> since it's not really related to the others.

Yes, will do.

> 
>>>> This patch will try to handle this case in a more common way instead of the
>>>> original 'arch' specific solution, which will be beneficial to all the
>>>> APEI-dependent platforms after that.
>>>
>>> This actually doesn't say anything about what the patch does or how it
>>> works.  It says "handles this case in a more common way" but with no
>>> details.
>>
>> Good suggestion, I'll give more details about that...
>>> The EINJ table contains "injection instructions" that can read or
>>> write "register regions" described by generic address structures (see
>>> ACPI v6.3, sec 18.6.2 and 18.6.3), and __einj_error_trigger() requests
>>> those register regions with request_mem_region() or request_region()
>>> before executing the injections instructions.
>>>
>>> IIUC, this patch basically says "if this region is part of the MCFG
>>> area, we don't need to reserve it." That leads to the questions of why
>>> we need to reserve *any* of the areas
>>
>> AFAIK, the MCFG area is reserved since the ECAM module will provide
>> a generic Kernel Programming Interfaces(KPI), e.g,
>> pci_generic_config_read(...), so all the drivers are allowed to
>> access the pci config space only by those KPIs in a consistent and
>> safe way, direct raw access will break the rule.  Correct me if I am
>> missing sth.
>>
>>> and why it's safe to simply skip reserving regions that are part
>>> of the MCFG area.
>>
>> Actual there is a commit d91525eb8ee6("ACPI, EINJ: Enhance error
>> injection tolerance level") before to address this issue, the entire
>> commit log as below:
>>
>>     Some BIOSes utilize PCI MMCFG space read/write opertion to trigger
>>     specific errors. EINJ will report errors as below when hitting such
>>     cases:
>>     
>>     APEI: Can not request [mem 0x83f990a0-0x83f990a3] for APEI EINJ Trigger registers
>>     
>>     It is because on x86 platform ACPI based PCI MMCFG logic has
>>     reserved all MMCFG spaces so that EINJ can't reserve it again.
>>     We already trust the ACPI/APEI code when using the EINJ interface
>>     so it is not a big leap to also trust it to access the right
>>     MMCFG addresses. Skip address checking to allow the access.
> 
> I'm not really convinced by that justification because I don't think
> the issue here is *trust*.  If all we care about is trust, and we
> trust the ACPI/APEI code, why do we need to reserve anything at all
> when executing EINJ actions?
> 
> I think the resource reservation issue is about coordinating multiple
> users of the address space.  A driver reserves the MMIO address space
> of a device it controls so no other driver can reserve it at the same
> time and cause conflicts.
> 
> I'm not really convinced by this mutual exclusion argument either,
> because I haven't yet seen a situation where we say "EINJ needs a
> resource that's already in use by somebody else, so we can't use
> EINJ."  When conflicts arise, the response is always "we'll just
> stop reserving this conflicting resource but use it anyway."
> 
> I think the only real value in apei_resources_request() is a little
> bit of documentation in /proc/iomem.  For ERST and EINJ, even that
> only lasts for the tiny period when we're actually executing an
> action.
> 
> So convince me there's a reason why we shouldn't just remove
> apei_resources_request() completely :)
> 

I have to confess that currently I have no strong evidence/reason to convince
you that it's absolute safe to remove apei_resources_request(),  probably in
some conditions it *does* require to follow the mutual exclusion usage model.
The ECAM/MCFG maybe a special case not like other normal device driver, since
all its MCFG space has been reserved during the initialization. Anyway, it's
another topic and good point well worth discussing in the future.

>From the patch set itself, I don't think it's a nice idea to make a dramatic
change regarding the apei_resources_request() part, I suggest to keep the original
rationale untouched and based on that to fix the real issue at hand in a more
generic way.

Any thought? If no objection, I plan to finalize the next version patch according
to the previous feedbacks and send it out for reviewing soon...

Thanks,
Xuesong

>> Except that the above explanation, IMO the EINJ is only a RAS debug
>> framework, in this code path, sometimes we need to acesss the
>> address within the MCFG space directly to trigger kind of HW error,
>> which behavior does not like the normal device driver's, in this
>> case some possible unsafe operations (bypass the ecam ops) can be
>> mitigated because the touched device will generate some HW errors
>> and the RAS handling part will preempt its corresponding drivers to
>> fix/log the HW error, that's my understanding about that.
> 
>>>> Signed-off-by: Xuesong Chen <xuesong.chen@...ux.alibaba.com>
>>>> Reported-by: kernel test robot <lkp@...el.com>
>>>> Reviewed-by: Lorenzo Pieralisi <lorenzo.pieralisi@....com>
>>>> Cc: Catalin Marinas <catalin.marinas@....com>
>>>> Cc: James Morse <james.morse@....com>
>>>> Cc: Will Deacon <will@...nel.org>
>>>> Cc: Rafael. J. Wysocki <rafael@...nel.org>
>>>> Cc: Tony Luck <tony.luck@...el.com>
>>>> Cc: Tomasz Nowicki <tn@...ihalf.com>
>>>> ---
>>>>  arch/x86/pci/mmconfig-shared.c | 28 --------------------------
>>>>  drivers/acpi/apei/apei-base.c  | 45 ++++++++++++++++++++++++++++--------------
>>>>  2 files changed, 30 insertions(+), 43 deletions(-)
>>>>
>>>> diff --git a/arch/x86/pci/mmconfig-shared.c b/arch/x86/pci/mmconfig-shared.c
>>>> index 0b961fe6..12f7d96 100644
>>>> --- a/arch/x86/pci/mmconfig-shared.c
>>>> +++ b/arch/x86/pci/mmconfig-shared.c
>>>> @@ -605,32 +605,6 @@ static int __init pci_parse_mcfg(struct acpi_table_header *header)
>>>>  	return 0;
>>>>  }
>>>>  
>>>> -#ifdef CONFIG_ACPI_APEI
>>>> -extern int (*arch_apei_filter_addr)(int (*func)(__u64 start, __u64 size,
>>>> -				     void *data), void *data);
>>>> -
>>>> -static int pci_mmcfg_for_each_region(int (*func)(__u64 start, __u64 size,
>>>> -				     void *data), void *data)
>>>> -{
>>>> -	struct pci_mmcfg_region *cfg;
>>>> -	int rc;
>>>> -
>>>> -	if (list_empty(&pci_mmcfg_list))
>>>> -		return 0;
>>>> -
>>>> -	list_for_each_entry(cfg, &pci_mmcfg_list, list) {
>>>> -		rc = func(cfg->res.start, resource_size(&cfg->res), data);
>>>> -		if (rc)
>>>> -			return rc;
>>>> -	}
>>>> -
>>>> -	return 0;
>>>> -}
>>>> -#define set_apei_filter() (arch_apei_filter_addr = pci_mmcfg_for_each_region)
>>>> -#else
>>>> -#define set_apei_filter()
>>>> -#endif
>>>> -
>>>>  static void __init __pci_mmcfg_init(int early)
>>>>  {
>>>>  	pci_mmcfg_reject_broken(early);
>>>> @@ -665,8 +639,6 @@ void __init pci_mmcfg_early_init(void)
>>>>  		else
>>>>  			acpi_table_parse(ACPI_SIG_MCFG, pci_parse_mcfg);
>>>>  		__pci_mmcfg_init(1);
>>>> -
>>>> -		set_apei_filter();
>>>>  	}
>>>>  }
>>>>  
>>>> diff --git a/drivers/acpi/apei/apei-base.c b/drivers/acpi/apei/apei-base.c
>>>> index c7fdb12..daae75a 100644
>>>> --- a/drivers/acpi/apei/apei-base.c
>>>> +++ b/drivers/acpi/apei/apei-base.c
>>>> @@ -21,6 +21,7 @@
>>>>  #include <linux/kernel.h>
>>>>  #include <linux/module.h>
>>>>  #include <linux/init.h>
>>>> +#include <linux/pci.h>
>>>>  #include <linux/acpi.h>
>>>>  #include <linux/slab.h>
>>>>  #include <linux/io.h>
>>>> @@ -448,13 +449,34 @@ static int apei_get_nvs_resources(struct apei_resources *resources)
>>>>  	return acpi_nvs_for_each_region(apei_get_res_callback, resources);
>>>>  }
>>>>  
>>>> -int (*arch_apei_filter_addr)(int (*func)(__u64 start, __u64 size,
>>>> -				     void *data), void *data);
>>>> -static int apei_get_arch_resources(struct apei_resources *resources)
>>>> +#ifdef CONFIG_PCI
>>>> +extern struct list_head pci_mmcfg_list;
>>>> +static int apei_filter_mcfg_addr(struct apei_resources *res,
>>>> +			struct apei_resources *mcfg_res)
>>>> +{
>>>> +	int rc = 0;
>>>> +	struct pci_mmcfg_region *cfg;
>>>> +
>>>> +	if (list_empty(&pci_mmcfg_list))
>>>> +		return 0;
>>>> +
>>>> +	apei_resources_init(mcfg_res);
>>>> +	list_for_each_entry(cfg, &pci_mmcfg_list, list) {
>>>> +		rc = apei_res_add(&mcfg_res->iomem, cfg->res.start, resource_size(&cfg->res));
>>>> +		if (rc)
>>>> +			return rc;
>>>> +	}
>>>>  
>>>> +	/* filter the mcfg resource from current APEI's */
>>>> +	return apei_resources_sub(res, mcfg_res);
>>>> +}
>>>> +#else
>>>> +static inline int apei_filter_mcfg_addr(struct apei_resources *res,
>>>> +			struct apei_resources *mcfg_res)
>>>>  {
>>>> -	return arch_apei_filter_addr(apei_get_res_callback, resources);
>>>> +	return 0;
>>>>  }
>>>> +#endif
>>>>  
>>>>  /*
>>>>   * IO memory/port resource management mechanism is used to check
>>>> @@ -486,15 +508,9 @@ int apei_resources_request(struct apei_resources *resources,
>>>>  	if (rc)
>>>>  		goto nvs_res_fini;
>>>>  
>>>> -	if (arch_apei_filter_addr) {
>>>> -		apei_resources_init(&arch_res);
>>>> -		rc = apei_get_arch_resources(&arch_res);
>>>> -		if (rc)
>>>> -			goto arch_res_fini;
>>>> -		rc = apei_resources_sub(resources, &arch_res);
>>>> -		if (rc)
>>>> -			goto arch_res_fini;
>>>> -	}
>>>> +	rc = apei_filter_mcfg_addr(resources, &arch_res);
>>>> +	if (rc)
>>>> +		goto arch_res_fini;
>>>>  
>>>>  	rc = -EINVAL;
>>>>  	list_for_each_entry(res, &resources->iomem, list) {
>>>> @@ -544,8 +560,7 @@ int apei_resources_request(struct apei_resources *resources,
>>>>  		release_mem_region(res->start, res->end - res->start);
>>>>  	}
>>>>  arch_res_fini:
>>>> -	if (arch_apei_filter_addr)
>>>> -		apei_resources_fini(&arch_res);
>>>> +	apei_resources_fini(&arch_res);
>>>>  nvs_res_fini:
>>>>  	apei_resources_fini(&nvs_resources);
>>>>  	return rc;
>>>> -- 
>>>> 1.8.3.1
>>>>

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