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

[Zhang, Jonathan Zhixiong]

Thanks Matt for the review. Yes, you are right on, I am following
this:
> modify ghes_ioremap_* to query the EFI memmap (if
> it's available at runtime) to lookup the correct mapping attributes.

Jonathan

On 6/5/2015 2:57 AM, Matt Fleming wrote:
> [ 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.

--
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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