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

["Zhang, Jonathan Zhixiong" <zjzhang@codeaurora.org>]

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