linux-kernel - Re: [PATCH RESEND] ACPI/Kconfig: Make ACPI_NFIT depend on EFI

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Date:	Tue, 15 Dec 2015 09:53:29 -0800
From:	Dan Williams <dan.j.williams@...el.com>
To:	Toshi Kani <toshi.kani@....com>
Cc:	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	"Elliott, Robert (Persistent Memory)" <elliott@....com>,
	"linux-nvdimm@...ts.01.org" <linux-nvdimm@...ts.01.org>,
	Linux ACPI <linux-acpi@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH RESEND] ACPI/Kconfig: Make ACPI_NFIT depend on EFI_STUB on X86

On Tue, Dec 15, 2015 at 9:49 AM, Toshi Kani <toshi.kani@....com> wrote:
> On Tue, 2015-12-15 at 09:21 -0800, Dan Williams wrote:
>> On Tue, Dec 15, 2015 at 8:59 AM, Toshi Kani <toshi.kani@....com> wrote:
>> > ACPI 6.0 defines NFIT table and new persistent memory types for
>> > EFI memory table (EFI_PERSISTENT_MEMORY) and e820 table (E820_PMEM).
>> >
>> > setup_e820() enabled by EFI_STUB converts EFI_PERSISTENT_MEMORY to
>> > E820_PMEM for the e820_map table on x86 EFI platforms.  When EFI_STUB
>> > is disabled, x86 kernels rely on the bootloader to perform this
>> > conversion.
>> >
>> > It was found that the upstream grub bootloader since 2012 has a bug
>> > that converts EFI_PERSISTENT_MEMORY (or any new type) to E820_RAM,
>> > which causes the kernel to use persistent memory ranges as regular
>> > memory and corrupts the data in NVDIMM.
>> >
>> > Therefore, this patch sets ACPI_NFIT to depend on EFI_STUB on x86.
>> > This assures that ACPI_NFIT kernels are self-contained and are
>> > protected from the upstream grub bug on x86.
>> >
>> > Note, X86_PMEM_LEGACY allows the kernel to use the pmem driver on
>> > pre-ACPI 6.0 platforms, and does not require ACPI_NFIT enabled.
>> >
>> > References:
>> > http://www.mail-archive.com/grub-devel@gnu.org/msg23961.html
>> > Reported-by: Robert Elliott <elliott@....com>
>> > Signed-off-by: Toshi Kani <toshi.kani@....com>
>> > Cc: Rafael J. Wysocki <rjw@...ysocki.net>
>> > Cc: Dan Williams <dan.j.williams@...el.com>
>> > ---
>> >  drivers/acpi/Kconfig |    1 +
>> >  1 file changed, 1 insertion(+)
>> >
>> > diff --git a/drivers/acpi/Kconfig b/drivers/acpi/Kconfig
>> > index 5eef4cb..5368baa 100644
>> > --- a/drivers/acpi/Kconfig
>> > +++ b/drivers/acpi/Kconfig
>> > @@ -441,6 +441,7 @@ config ACPI_NFIT
>> >         depends on PHYS_ADDR_T_64BIT
>> >         depends on BLK_DEV
>> >         depends on ARCH_HAS_MMIO_FLUSH
>> > +       depends on !X86 || (X86 && EFI_STUB)
>> >         select LIBNVDIMM
>> >         help
>> >           Infrastructure to probe ACPI 6 compliant platforms for
>>
>> This seems wrong to me.
>>
>> In general Kconfig "depends on" are only about compile-time code
>> dependency, not about working around random bugs in external projects.
>
> I agree that they do not have a compile dependency, and it looks rather
> odd.  On the other hand, proper support of the ACPI NFIT extensions has a
> functional dependency to setup_e820() as this is the only code that can
> handle the EFI_PERSISTENT_MEMORY type today.

What about non-EFI/legeacy-boot systems that only emit e820-type-7?
We lose support for them with this patch, right?
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