linux-kernel - Re: [PATCH] X86: don't print a warning when MTRR are blank and running in KVM

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Message-ID: <20080222111804.GB6504@amd.com>
Date:	Fri, 22 Feb 2008 12:18:04 +0100
From:	"Joerg Roedel" <joerg.roedel@....com>
To:	"Yinghai Lu" <yhlu.kernel@...il.com>
cc:	tglx@...utronix.de, mingo@...hat.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] X86: don't print a warning when MTRR are blank and
 running in KVM

On Thu, Feb 21, 2008 at 11:54:00AM -0800, Yinghai Lu wrote:
> On Thu, Feb 21, 2008 at 6:50 AM, Joerg Roedel <joerg.roedel@....com> wrote:
> > Inside a KVM virtual machine the MTRRs are usually blank. This confuses Linux
> >  and causes a warning message at boot. This patch removes that warning message
> >  when running Linux as a KVM guest.
> >
> >  Signed-off-by: Joerg Roedel <joerg.roedel@....com>
> >  ---
> >   arch/x86/kernel/cpu/mtrr/main.c |    7 +++++--
> >   1 files changed, 5 insertions(+), 2 deletions(-)
> >
> >  diff --git a/arch/x86/kernel/cpu/mtrr/main.c b/arch/x86/kernel/cpu/mtrr/main.c
> >  index b6e136f..47e624c 100644
> >  --- a/arch/x86/kernel/cpu/mtrr/main.c
> >  +++ b/arch/x86/kernel/cpu/mtrr/main.c
> >  @@ -43,6 +43,7 @@
> >   #include <asm/uaccess.h>
> >   #include <asm/processor.h>
> >   #include <asm/msr.h>
> >  +#include <asm/kvm_para.h>
> >   #include "mtrr.h"
> >
> >   u32 num_var_ranges = 0;
> >  @@ -687,12 +688,14 @@ int __init mtrr_trim_uncached_memory(unsigned long end_pfn)
> >         }
> >
> >         /* kvm/qemu doesn't have mtrr set right, don't trim them all */
> >  -       if (!highest_pfn) {
> >  +       if (!highest_pfn && !kvm_para_available()) {
> >                 printk(KERN_WARNING "WARNING: strange, CPU MTRRs all blank?\n");
> >                 WARN_ON(1);
> >  -               return 0;
> >         }
> >
> >  +       if (!highest_pfn)
> >  +               return 0;
> >  +
> >         if (highest_pfn < end_pfn) {
> >                 printk(KERN_WARNING "WARNING: BIOS bug: CPU MTRRs don't cover"
> >                         " all of memory, losing %luMB of RAM.\n",
> >  --
> >  1.5.3.7
> >
> 
> Doest that WARN_ON(1) hurt?

Yes. It inidicates a problem where there isn't one. In a virtual machine
MTRRs make absolutly no sense and so they should all be blank there.

Joerg

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