linux-kernel - Re: [Xen-devel] [PATCH] xen: fix dom0 boot on huge systems

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Date:   Thu, 07 Mar 2019 03:45:54 -0700
From:   "Jan Beulich" <JBeulich@...e.com>
To:     "Juergen Gross" <jgross@...e.com>
Cc:     "Borislav Petkov" <bp@...en8.de>,
        "Stefano Stabellini" <sstabellini@...nel.org>,
        "the arch/x86 maintainers" <x86@...nel.org>, <tglx@...utronix.de>,
        "xen-devel" <xen-devel@...ts.xenproject.org>,
        "Boris Ostrovsky" <boris.ostrovsky@...cle.com>, <mingo@...hat.com>,
        <linux-kernel@...r.kernel.org>, <hpa@...or.com>
Subject: Re: [Xen-devel] [PATCH] xen: fix dom0 boot on huge systems

>>> On 07.03.19 at 10:11, <jgross@...e.com> wrote:
> Commit f7c90c2aa40048 ("x86/xen: don't write ptes directly in 32-bit
> PV guests") introduced a regression for booting dom0 on huge systems
> with lots of RAM (in the TB range).
> 
> Reason is that on those hosts the p2m list needs to be moved early in
> the boot process and this requires temporary page tables to be created.
> Said commit modified xen_set_pte_init() to use a hypercall for writing
> a PTE, but this requires the page table being in the direct mapped
> area, which is not the case for the temporary page tables used in
> xen_relocate_p2m().
> 
> As the page tables are completely written before being linked to the
> actual address space instead of set_pte() a plain write to memory can
> be used in xen_relocate_p2m().
> 
> Fixes: f7c90c2aa40048 ("x86/xen: don't write ptes directly in 32-bit PV guests")
> Signed-off-by: Juergen Gross <jgross@...e.com>

Reviewed-by: Jan Beulich <jbeulich@...e.com>