Re: [PATCH] x86-64: make enabling of MMCFG on AMD Fam10 CPUsactually work

From: Ingo Molnar
Date: Thu Jul 21 2011 - 03:17:28 EST

* Jan Beulich <JBeulich@xxxxxxxxxx> wrote:

> Forcibly enabling the MMCFG space on AMD Fam10 CPUs cannot be expected
> to work, since with the firmware not being aware of the address range
> used, it cannot possibly reserve the space in E820 or ACPI resources.
> Hence we need to manually insert the range into the E820 table, and
> enable the range only when the insertion actually works without
> conflict.
> Adding the calls to the respective E820 handling functions additionally
> requires to deal with modpost's mismatch checking: The function doing
> those calls needs to be __init, and it is being made sure that it gets
> called (from its __cpuinit caller) only on the BSP, and through a stub
> (silencing the warning).
> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxxxx>
> Cc: Yinghai Lu <yinghai@xxxxxxxxxx>
> ---
> arch/x86/kernel/mmconf-fam10h_64.c | 22 +++++++++++++++++++---
> 1 file changed, 19 insertions(+), 3 deletions(-)

I agree with the patch (and please also add the second fix you
extracted from Yinghai's patch, as a second patch).

This changelog is missing scope analysis: what systems are affected
in practice (if any), were actual problems observed, if no problems
were observed then what are the potential problems that people should
look out for (and which this commit may fix), etc.

If none of that information is available then such a small blurb:

'This bug was found via code review and I'm not aware of any systems
that are affected currently - but some may exist.'

Will inform maintainers and other interested parties about the
practical background of the patch.


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