linux-kernel - Re: [Patch v3 01/14] x86/ioremap: Fix page aligned size calculation in __ioremap

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Message-ID: <Y3vVRnAZmDCyQ3Wo@zn.tnic>
Date:   Mon, 21 Nov 2022 20:45:10 +0100
From:   Borislav Petkov <bp@...en8.de>
To:     "Michael Kelley (LINUX)" <mikelley@...rosoft.com>
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Subject: Re: [Patch v3 01/14] x86/ioremap: Fix page aligned size calculation
 in __ioremap_caller()

On Mon, Nov 21, 2022 at 04:40:16PM +0000, Michael Kelley (LINUX) wrote:
> As discussed in a parallel thread [1], the incorrect code here doesn't have
> any real impact in already released Linux kernels.  It only affects the
> transition that my patch series implements to change the way vTOM
> is handled.

Are you sure?

PHYSICAL_PAGE_MASK is controlled by __PHYSICAL_MASK which is determined
by CONFIG_DYNAMIC_PHYSICAL_MASK and __PHYSICAL_MASK_SHIFT which all
differ depending on configurations and also dynamic.

It is probably still ok, in probably all possible cases even though I
wouldn't bet on it.

And this fix is simple and all clear so lemme ask it differently: what
would be any downsides in backporting it to stable, just in case?

> I don't know what the tradeoffs are for backporting a fix that doesn't solve
> a real problem vs. just letting it be.  Every backport carries some overhead
> in the process

Have you seen the deluge of stable fixes? :-)

> and there's always a non-zero risk of breaking something.

I don't see how this one would cause any breakage...

> I've leaned away from adding the "Fixes:" tag in such cases. But if
> it's better to go ahead and add the "Fixes:" tag for what's only a
> theoretical problem, I'm OK with doing so.

I think this is a good to have fix anyway as it is Obviously
Correct(tm).

Unless you have any reservations you haven't shared yet...

> [1] https://lkml.org/lkml/2022/11/11/1348

Btw, the proper way to reference to a mail message now is simply to do:

https://lore.kernel.org/r/<Message-ID>

as long as it has been posted on some ML which lore archives. And I
think it archives all.

Thx.

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette