linux-kernel - Re: [PATCH v2] xen/pv: Call get_cpu_address_sizes to set x86_virt/phys

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Date:   Tue, 24 Jul 2018 10:08:19 -0400
From:   Boris Ostrovsky <boris.ostrovsky@...cle.com>
To:     "M. Vefa Bicakci" <m.v.b@...box.com>, linux-kernel@...r.kernel.org
Cc:     "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Andy Lutomirski <luto@...nel.org>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Juergen Gross <jgross@...e.com>,
        xen-devel@...ts.xenproject.org, x86@...nel.org,
        stable@...r.kernel.org
Subject: Re: [PATCH v2] xen/pv: Call get_cpu_address_sizes to set
 x86_virt/phys_bits

On 07/24/2018 08:45 AM, M. Vefa Bicakci wrote:
> Commit d94a155c59c9 ("x86/cpu: Prevent cpuinfo_x86::x86_phys_bits
> adjustment corruption") has moved the query and calculation of the
> x86_virt_bits and x86_phys_bits fields of the cpuinfo_x86 struct
> from the get_cpu_cap function to a new function named
> get_cpu_address_sizes.
>
> One of the call sites related to Xen PV VMs was unfortunately missed
> in the aforementioned commit. This prevents successful boot-up of
> kernel versions 4.17 and up in Xen PV VMs if CONFIG_DEBUG_VIRTUAL
> is enabled, due to the following code path:
>
>   enlighten_pv.c::xen_start_kernel
>     mmu_pv.c::xen_reserve_special_pages
>       page.h::__pa
>         physaddr.c::__phys_addr
>           physaddr.h::phys_addr_valid
>
> phys_addr_valid uses boot_cpu_data.x86_phys_bits to validate physical
> addresses. boot_cpu_data.x86_phys_bits is no longer populated before
> the call to xen_reserve_special_pages due to the aforementioned commit
> though, so the validation performed by phys_addr_valid fails, which
> causes __phys_addr to trigger a BUG, preventing boot-up.
>
> Signed-off-by: M. Vefa Bicakci <m.v.b@...box.com>
> Cc: "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
> Cc: Andy Lutomirski <luto@...nel.org>
> Cc: Ingo Molnar <mingo@...hat.com>
> Cc: "H. Peter Anvin" <hpa@...or.com>
> Cc: Thomas Gleixner <tglx@...utronix.de>
> Cc: Boris Ostrovsky <boris.ostrovsky@...cle.com>
> Cc: Juergen Gross <jgross@...e.com>
> Cc: xen-devel@...ts.xenproject.org
> Cc: x86@...nel.org
> Cc: stable@...r.kernel.org # for v4.17 and up
> Fixes: d94a155c59c9 ("x86/cpu: Prevent cpuinfo_x86::x86_phys_bits adjustment corruption")

Reviewed-by: Boris Ostrovsky <boris.ostrovsky@...cle.com>