linux-kernel - Re: [PATCH] x86/kexec: always ensure EFI systab region is mapped

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Message-ID: <20190423104924.GA1730@dhcp-128-65.nay.redhat.com>
Date:   Tue, 23 Apr 2019 18:49:24 +0800
From:   Dave Young <dyoung@...hat.com>
To:     Junichi Nomura <j-nomura@...jp.nec.com>
Cc:     Kairui Song <kasong@...hat.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Borislav Petkov <bp@...en8.de>,
        Thomas Gleixner <tglx@...utronix.de>,
        Chao Fan <fanc.fnst@...fujitsu.com>,
        Baoquan He <bhe@...hat.com>, "x86@...nel.org" <x86@...nel.org>,
        "kexec@...ts.infradead.org" <kexec@...ts.infradead.org>
Subject: Re: [PATCH] x86/kexec: always ensure EFI systab region is mapped

On 04/23/19 at 06:20am, Junichi Nomura wrote:
> On 4/22/19 6:28 PM, Kairui Song wrote:
> > The reason is the systab region is not mapped by the identity mapping
> > provided by kexec. Currently kexec only create identity mapping for
> > mem regions, wihch won't cover the systab. So second kernel will be
> > accessing a not mapped memory region and cause fault.
> > But as kexec tend to pad the map region up to PUD size, the
> > systab could be included in the map by accident, so it worked on
> > some machines, but that will be broken easily and unstable.
> 
> Is the mapping of ACPI tables just by luck, too?

Hmm, guess it should be mapped by luck, here is the range on the T420: 
da99f000 - dae9efff Reserved (efi systab fall in this region)
daf9f000 - daffefff ACPI tables

Thanks
Dave