Re: [PATCH V2 3/3] acpi, apei: use EFI memmap to map GHES memory

[Matt Fleming]

[ Cc'ing Boris and Tony. Folks original patch is here,
  https://lkml.kernel.org/r/1433185940-24770-4-git-send-email-zjzhang@xxxxxxxxxxxxxx ]

On Mon, 01 Jun, at 12:12:20PM, Jonathan (Zhixiong) Zhang wrote:
> From: "Jonathan (Zhixiong) Zhang" <zjzhang@xxxxxxxxxxxxxx>
> 
> With ACPI APEI firmware first handling, generic hardware error
> record is updated by firmware in GHES memory region. When firmware
> updated GHES memory region in DDR without going through cache,
> Linux reads stale data from cache.
> 
> GHES memory region should be mapped with cache attributes
> according to EFI memory map when applicable. If firmware updates
> DDR directly, EFI memory map has GHES memory region defined as
> uncached; If firmware updates cache, EFI memory map has GHES
> memory region defined as cached.
> 
> When EFI is configued, map IRQ page using efi_remap() provided by
> EFI subsystem.

[...]

> @@ -159,6 +160,7 @@ static void __iomem *ghes_ioremap_pfn_nmi(u64 pfn)
>  	return (void __iomem *)vaddr;
>  }
>  
> +#ifndef CONFIG_EFI
>  static void __iomem *ghes_ioremap_pfn_irq(u64 pfn)
>  {
>  	unsigned long vaddr;

Sprinkling CONFIG_EFI like this is wrong. On x86 we run kernels built
with CONFIG_EFI on machines with BIOS - you can't make the EFI vs.
non-EFI decision at compile-time.

So this patch looks like a potential regression to me since on x86
ghes_ioremap_pfn_irq() would not be used anymore and instead we'd be
using efi_remap() which will perform an ioremap_nocache() if it gets
called after efi_free_boot_services().

And based on the comments in the apei code, that's going to cause issues
because ioremap() does not work in atomic context, not to mention the
fact that we've gone from a cached mapping to an uncached one.

Instead, I suggest you modify ghes_ioremap_* to query the EFI memmap (if
it's available at runtime) to lookup the correct mapping attributes.

But I've Cc'd some more people who have actually worked on this code,
since I'm not one of them.

-- 
Matt Fleming, Intel Open Source Technology Center
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