linux-kernel - Re: [PATCH] x86/setup: call early_reserve

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Date:   Thu, 16 Sep 2021 12:09:27 +0300
From:   Mike Rapoport <rppt@...nel.org>
To:     Borislav Petkov <bp@...en8.de>
Cc:     Juergen Gross <jgross@...e.com>, Jan Beulich <jbeulich@...e.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        Marek Marczykowski-Górecki 
        <marmarek@...isiblethingslab.com>, xen-devel@...ts.xenproject.org,
        x86@...nel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] x86/setup: call early_reserve_memory() earlier

On Wed, Sep 15, 2021 at 01:00:20PM +0200, Borislav Petkov wrote:
> You forgot to Cc Mike, lemme add him.
> 
> And drop stable@ too.
> 
> On Tue, Sep 14, 2021 at 01:06:22PM +0200, Juergen Gross wrote:
> > On 14.09.21 12:03, Jan Beulich wrote:
> > > On 14.09.2021 11:41, Juergen Gross wrote:
> > > > Commit a799c2bd29d19c565 ("x86/setup: Consolidate early memory
> > > > reservations") introduced early_reserve_memory() to do all needed
> > > > initial memblock_reserve() calls in one function. Unfortunately the
> > > > call of early_reserve_memory() is done too late for Xen dom0, as in
> > > > some cases a Xen hook called by e820__memory_setup() will need those
> > > > memory reservations to have happened already.
> > > > 
> > > > Move the call of early_reserve_memory() to the beginning of
> > > > setup_arch() in order to avoid such problems.
> > > > 
> > > > Cc: stable@...r.kernel.org
> > > > Fixes: a799c2bd29d19c565 ("x86/setup: Consolidate early memory reservations")
> > > > Reported-by: Marek Marczykowski-Górecki <marmarek@...isiblethingslab.com>
> > > > Signed-off-by: Juergen Gross <jgross@...e.com>
> > > > ---
> > > >   arch/x86/kernel/setup.c | 24 ++++++++++++------------
> > > >   1 file changed, 12 insertions(+), 12 deletions(-)
> > > > 
> > > > diff --git a/arch/x86/kernel/setup.c b/arch/x86/kernel/setup.c
> > > > index 79f164141116..f369c51ec580 100644
> > > > --- a/arch/x86/kernel/setup.c
> > > > +++ b/arch/x86/kernel/setup.c
> > > > @@ -757,6 +757,18 @@ dump_kernel_offset(struct notifier_block *self, unsigned long v, void *p)
> > > >   void __init setup_arch(char **cmdline_p)
> > > >   {
> > > > +	/*
> > > > +	 * Do some memory reservations *before* memory is added to
> > > > +	 * memblock, so memblock allocations won't overwrite it.
> > > > +	 * Do it after early param, so we could get (unlikely) panic from
> > > > +	 * serial.
> > > 
> > > Hmm, this part of the comment is not only stale now, but gets actively
> > > undermined. No idea how likely such a panic() would be, and hence how
> > > relevant it is to retain this particular property.
> > 
> > Ah, right.
> > 
> > The alternative would be to split it up again. Let's let the x86
> > maintainers decide which way is the better one.

I think the first sentence about reserving memory before memblock
allocations are possible is important and I think we should keep it.

With that

Acked-by: Mike Rapoport <rppt@...ux.ibm.com>

> > 
> > 
> > Juergen
> > 
> > > 
> > > Jan
> > > 
> > > > +	 * After this point everything still needed from the boot loader or
> > > > +	 * firmware or kernel text should be early reserved or marked not
> > > > +	 * RAM in e820. All other memory is free game.
> > > > +	 */
> > > > +	early_reserve_memory();
> > > > +
> > > >   #ifdef CONFIG_X86_32
> > > >   	memcpy(&boot_cpu_data, &new_cpu_data, sizeof(new_cpu_data));
> > > > @@ -876,18 +888,6 @@ void __init setup_arch(char **cmdline_p)
> > > >   	parse_early_param();
> > > > -	/*
> > > > -	 * Do some memory reservations *before* memory is added to
> > > > -	 * memblock, so memblock allocations won't overwrite it.
> > > > -	 * Do it after early param, so we could get (unlikely) panic from
> > > > -	 * serial.
> > > > -	 *
> > > > -	 * After this point everything still needed from the boot loader or
> > > > -	 * firmware or kernel text should be early reserved or marked not
> > > > -	 * RAM in e820. All other memory is free game.
> > > > -	 */
> > > > -	early_reserve_memory();
> > > > -
> > > >   #ifdef CONFIG_MEMORY_HOTPLUG
> > > >   	/*
> > > >   	 * Memory used by the kernel cannot be hot-removed because Linux
> > > > 
> > > 
> > 
> 
> 
> 
> 
> 
> 
> -- 
> Regards/Gruss,
>     Boris.
> 
> https://people.kernel.org/tglx/notes-about-netiquette

-- 
Sincerely yours,
Mike.