linux-kernel - Re: [PATCHv7] x86/kdump: bugfix, make the behavior of crashkernel=X consistent with kaslr

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Date:   Fri, 1 Mar 2019 11:19:15 +0800
From:   Pingfan Liu <kernelfans@...il.com>
To:     Borislav Petkov <bp@...en8.de>
Cc:     Dave Young <dyoung@...hat.com>, Joerg Roedel <jroedel@...e.de>,
        Baoquan He <bhe@...hat.com>,
        Jerry Hoemann <jerry.hoemann@....com>, x86@...nel.org,
        Randy Dunlap <rdunlap@...radead.org>,
        kexec@...ts.infradead.org, LKML <linux-kernel@...r.kernel.org>,
        Mike Rapoport <rppt@...ux.vnet.ibm.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Yinghai Lu <yinghai@...nel.org>, vgoyal@...hat.com,
        iommu@...ts.linux-foundation.org, konrad.wilk@...cle.com
Subject: Re: [PATCHv7] x86/kdump: bugfix, make the behavior of crashkernel=X
 consistent with kaslr

On Fri, Mar 1, 2019 at 11:04 AM Pingfan Liu <kernelfans@...il.com> wrote:
>
> Hi Borislav,
>
> Do you think the following patch is good at present?
> diff --git a/arch/x86/kernel/setup.c b/arch/x86/kernel/setup.c
> index 81f9d23..9213073 100644
> --- a/arch/x86/kernel/setup.c
> +++ b/arch/x86/kernel/setup.c
> @@ -460,7 +460,7 @@ static void __init
> memblock_x86_reserve_range_setup_data(void)
>  # define CRASH_ADDR_LOW_MAX    (512 << 20)
>  # define CRASH_ADDR_HIGH_MAX   (512 << 20)
>  #else
> -# define CRASH_ADDR_LOW_MAX    (896UL << 20)
> +# define CRASH_ADDR_LOW_MAX    (1 << 32)
>  # define CRASH_ADDR_HIGH_MAX   MAXMEM
>  #endif
>
Or patch lools like:
diff --git a/arch/x86/kernel/setup.c b/arch/x86/kernel/setup.c
index 3d872a5..ed0def5 100644
--- a/arch/x86/kernel/setup.c
+++ b/arch/x86/kernel/setup.c
@@ -459,7 +459,7 @@ static void __init
memblock_x86_reserve_range_setup_data(void)
 # define CRASH_ADDR_LOW_MAX    (512 << 20)
 # define CRASH_ADDR_HIGH_MAX   (512 << 20)
 #else
-# define CRASH_ADDR_LOW_MAX    (896UL << 20)
+# define CRASH_ADDR_LOW_MAX    (1 << 32)
 # define CRASH_ADDR_HIGH_MAX   MAXMEM
 #endif

@@ -551,6 +551,15 @@ static void __init reserve_crashkernel(void)
                                                    high ? CRASH_ADDR_HIGH_MAX
                                                         : CRASH_ADDR_LOW_MAX,
                                                    crash_size, CRASH_ALIGN);
+#ifdef CONFIG_X86_64
+               /*
+                * crashkernel=X reserve below 4G fails? Try MAXMEM
+                */
+               if (!high && !crash_base)
+                       crash_base = memblock_find_in_range(CRASH_ALIGN,
+                                               CRASH_ADDR_HIGH_MAX,
+                                               crash_size, CRASH_ALIGN);
+#endif

which tries 0-4G, the fall back to 4G above

> For documentation, I will send another patch to improve the description.
>
> Thanks,
> Pingfan
>
> On Mon, Feb 25, 2019 at 7:30 PM Borislav Petkov <bp@...en8.de> wrote:
> >
> > On Mon, Feb 25, 2019 at 07:12:16PM +0800, Dave Young wrote:
> > > If we move to high as default, it will allocate 160M high + 256M low. It
> >
> > We won't move to high by default - we will *fall* back to high if the
> > default allocation fails.
> >
> > > To make the process less fragile maybe we can remove the 896M limitation
> > > and only try <4G then go to high.
> >
> > Sure, the more robust for the user, the better.
> >
> > --
> > Regards/Gruss,
> >     Boris.
> >
> > Good mailing practices for 400: avoid top-posting and trim the reply.