linux-kernel - Re: [RFC][PATCH 02/34] x86/xen: Remove early "debug" physical address lookups

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Date: Mon, 11 Mar 2024 14:16:09 +0100
From: Jürgen Groß <jgross@...e.com>
To: Dave Hansen <dave.hansen@...ux.intel.com>, linux-kernel@...r.kernel.org
Cc: kirill.shutemov@...ux.intel.com, pbonzini@...hat.com, tglx@...utronix.de,
 x86@...nel.org, bp@...en8.de
Subject: Re: [RFC][PATCH 02/34] x86/xen: Remove early "debug" physical address
 lookups

On 22.02.24 19:39, Dave Hansen wrote:
> From: Dave Hansen <dave.hansen@...ux.intel.com>
> 
> The __pa() facility is subject to debugging checks if CONFIG_DEBUG_VIRTUAL=y.
> One of those debugging checks is whether the physical address is valid
> on the platform.  That information is normally available via CPUID.  But
> the __pa() code currently looks it up in 'boot_cpu_data' which is not
> fully set up in early Xen PV boot.
> 
> The Xen PV code currently tries to get this info with
> get_cpu_address_sizes() which also depends on 'boot_cpu_data' to be at
> least somewhat set up.  The result is that the c->x86_phys_bits gets a
> sane value, but not one that has anything to do with the hardware.  In
> other words, the CONFIG_DEBUG_VIRTUAL checks are performed with what
> amounts to garbage inputs.
> 
> Garbage checks are worse than no check at all.  Move over to the
> "nodebug" variant to axe the checks.
> 
> Signed-off-by: Dave Hansen <dave.hansen@...ux.intel.com>
> Cc: Juergen Gross <jgross@...e.com>

Reviewed-by: Juergen Gross <jgross@...e.com>


Juergen