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Re: [PATCH V3 4/4] acpi, apei: use EFI memmap to map GHES memory

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  Re: [PATCH V3 4/4] acpi, apei: use EFI memmap to map GHES memory "Zhang, Jonathan Zhixiong" <zjzhang@codeaurora.org> - 2015-06-13 01:50 +0200
    Re: [PATCH V3 4/4] acpi, apei: use EFI memmap to map GHES memory Borislav Petkov <bp@alien8.de> - 2015-06-13 10:30 +0200
      Re: [PATCH V3 4/4] acpi, apei: use EFI memmap to map GHES memory Matt Fleming <matt@codeblueprint.co.uk> - 2015-06-22 07:20 +0200

#1164439 — Re: [PATCH V3 4/4] acpi, apei: use EFI memmap to map GHES memory

On 6/12/2015 9:29 AM, Borislav Petkov wrote:
> On Thu, Jun 11, 2015 at 11:26:00AM -0700, Jonathan (Zhixiong) Zhang wrote:
>> From: "Jonathan (Zhixiong) Zhang" <zjzhang@codeaurora.org>
>>
>> With ACPI APEI firmware first handling, generic hardware error
>> record is updated by firmware in GHES memory region. When firmware
>> updated GHES memory region with uncached access attribute, Linux
>> reads stale data from cache.
>>
>> GHES memory region should be mapped with cache attributes
>> according to EFI memory map when applicable. On such system, if
>> firmware updates RAM directly without going through cache,
>> EFI memory map has GHES memory region defined as uncached;
>> If firmware updates cache, EFI memory map has GHES memory region
>> defined as cached.
>>
>> On EFI system, if GHES memory region has EFI_MEMORY_UC attribute
>> defined, map the page with arch defined UC page protection type.
>>
>> Signed-off-by: Jonathan (Zhixiong) Zhang <zjzhang@codeaurora.org>
>> ---
>>   drivers/acpi/apei/ghes.c | 9 ++++++++-
>>   1 file changed, 8 insertions(+), 1 deletion(-)
>>
>> diff --git a/drivers/acpi/apei/ghes.c b/drivers/acpi/apei/ghes.c
>> index e82d0976a5d0..5cfd951ebf67 100644
>> --- a/drivers/acpi/apei/ghes.c
>> +++ b/drivers/acpi/apei/ghes.c
>> @@ -48,6 +48,7 @@
>>   #include <linux/pci.h>
>>   #include <linux/aer.h>
>>   #include <linux/nmi.h>
>> +#include <linux/efi.h>
>>
>>   #include <acpi/ghes.h>
>>   #include <acpi/apei.h>
>> @@ -164,8 +165,14 @@ static void __iomem *ghes_ioremap_pfn_irq(u64 pfn)
>>   	unsigned long vaddr;
>>
>>   	vaddr = (unsigned long)GHES_IOREMAP_IRQ_PAGE(ghes_ioremap_area->addr);
>> -	ioremap_page_range(vaddr, vaddr + PAGE_SIZE,
>> +
>> +	if (efi_mem_attributes(pfn << PAGE_SHIFT) & EFI_MEMORY_UC) {
>> +		ioremap_page_range(vaddr, vaddr + PAGE_SIZE,
>> +				   pfn << PAGE_SHIFT, ARCH_APEI_PAGE_KERNEL_UC);
>> +	} else {
>> +		ioremap_page_range(vaddr, vaddr + PAGE_SIZE,
>>   			   pfn << PAGE_SHIFT, PAGE_KERNEL);
>> +	}
>>
>>   	return (void __iomem *)vaddr;
>
> This is still hacky. All of a sudden, ghes code gets to know about EFI
> which looks like a mishmash to me.
>
> Maybe it would be cleaner if you added an arch-specific
>
> 	arch_get_mem_attribute(phys_addr);
>
> which returns a pgprot_t thing which you can use directly above, like
> so:
>
>          ioremap_page_range(vaddr,
> 			   vaddr + PAGE_SIZE,
>                             pfn << PAGE_SHIFT,
> 			   arch_get_mem_attribute(pfn << PAGE_SHIFT));
>
> Each arch can then return what it likes with arch_get_mem_attribute().
 >
Thanks for the review, Borislav. I will do that. Since such function
is only needed for APEI functionality, at least as of today, I will
name it arch_apei_get_mem_attribute().
I will add implementations for arm64 and x86 since those are the only
archs having HAVE_ACPI_APEI defined in Kconfig. The upstream kernel
today does not have HAVE_ACPI_APEI defined for arm64, but it needs to
be and will be.

-- 
Jonathan (Zhixiong) Zhang
The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum,
a Linux Foundation Collaborative Project
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#1164591

On Fri, Jun 12, 2015 at 04:44:25PM -0700, Zhang, Jonathan Zhixiong wrote:
> Since such function is only needed for APEI functionality, at least as
> of today, I will name it arch_apei_get_mem_attribute().

Why?

It can be extended to be used generically too, no? Come to think of it,
the different arches should already have a way to tell you with what mem
attributes a physical address is mapped, no?

IOW, such functionality should be already present, you'd only have to
find it and use it.

-- 
Regards/Gruss,
    Boris.

ECO tip #101: Trim your mails when you reply.
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#1169693

On Mon, 15 Jun, at 04:59:08PM, Borislav Petkov wrote:
> On Mon, Jun 15, 2015 at 03:15:33PM +0100, Matt Fleming wrote:
> > On Sat, 13 Jun, at 10:27:51AM, Borislav Petkov wrote:
> > > On Fri, Jun 12, 2015 at 04:44:25PM -0700, Zhang, Jonathan Zhixiong wrote:
> > > > Since such function is only needed for APEI functionality, at least as
> > > > of today, I will name it arch_apei_get_mem_attribute().
> > > 
> > > Why?
> > > 
> > > It can be extended to be used generically too, no? Come to think of it,
> > > the different arches should already have a way to tell you with what mem
> > > attributes a physical address is mapped, no?
> > > 
> > > IOW, such functionality should be already present, you'd only have to
> > > find it and use it.
> > 
> > I did think about this, but I don't think we have a generic way to ask
> > the firmware for its memory map.
> 
> Not the firmware but the OS. Like on x86, for example, we have MTRRs
> and PAT and they cover the whole range. Basically what lookup_memtype()
> does. We already have that info, why not query it instead of growing
> more stuff ontop.
> 
> I mean, we do ioremap* which does reserve_memtype() and sticks the range
> in the rbtree which we query after. Can't be better than that...

Right, but see my previous comment about x86 discarding a bunch of
attributes for memory regions because the kernel "knows better".

And in most places, yes, the kernel really does know better. But this
APEI case is special because irrespective of what the kernel says we
want to be compatible with the firmware's memory map.

And we don't have an API for that.

-- 
Matt Fleming, Intel Open Source Technology Center
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