linux-kernel - Re: [RFC PATCH v4 26/28] x86: Allow kexec to be used with SME

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Message-ID: <20170301092536.GB8353@dhcp-128-65.nay.redhat.com>
Date:   Wed, 1 Mar 2017 17:25:36 +0800
From:   Dave Young <dyoung@...hat.com>
To:     Tom Lendacky <thomas.lendacky@....com>
Cc:     Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
        linux-arch@...r.kernel.org, linux-efi@...r.kernel.org,
        kvm@...r.kernel.org, linux-doc@...r.kernel.org, x86@...nel.org,
        linux-kernel@...r.kernel.org, kasan-dev@...glegroups.com,
        linux-mm@...ck.org, iommu@...ts.linux-foundation.org,
        Rik van Riel <riel@...hat.com>,
        Radim Krčmář <rkrcmar@...hat.com>,
        Toshimitsu Kani <toshi.kani@....com>,
        Arnd Bergmann <arnd@...db.de>,
        Jonathan Corbet <corbet@....net>,
        Matt Fleming <matt@...eblueprint.co.uk>,
        "Michael S. Tsirkin" <mst@...hat.com>,
        Joerg Roedel <joro@...tes.org>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Brijesh Singh <brijesh.singh@....com>,
        Ingo Molnar <mingo@...hat.com>,
        Alexander Potapenko <glider@...gle.com>,
        Andy Lutomirski <luto@...nel.org>,
        "H. Peter Anvin" <hpa@...or.com>, Borislav Petkov <bp@...en8.de>,
        Andrey Ryabinin <aryabinin@...tuozzo.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Larry Woodman <lwoodman@...hat.com>,
        Dmitry Vyukov <dvyukov@...gle.com>
Subject: Re: [RFC PATCH v4 26/28] x86: Allow kexec to be used with SME

Hi Tom,

On 02/17/17 at 10:43am, Tom Lendacky wrote:
> On 2/17/2017 9:57 AM, Konrad Rzeszutek Wilk wrote:
> > On Thu, Feb 16, 2017 at 09:47:55AM -0600, Tom Lendacky wrote:
> > > Provide support so that kexec can be used to boot a kernel when SME is
> > > enabled.
> > 
> > Is the point of kexec and kdump to ehh, dump memory ? But if the
> > rest of the memory is encrypted you won't get much, will you?
> 
> Kexec can be used to reboot a system without going back through BIOS.
> So you can use kexec without using kdump.
> 
> For kdump, just taking a quick look, the option to enable memory
> encryption can be provided on the crash kernel command line and then

Is there a simple way to get the SME status? Probably add some sysfs
file for this purpose.

> crash kernel can would be able to copy the memory decrypted if the
> pagetable is set up properly. It looks like currently ioremap_cache()
> is used to map the old memory page.  That might be able to be changed
> to a memremap() so that the encryption bit is set in the mapping. That
> will mean that memory that is not marked encrypted (EFI tables, swiotlb
> memory, etc) would not be read correctly.

Manage to store info about those ranges which are not encrypted so that
memremap can handle them?

> 
> > 
> > Would it make sense to include some printk to the user if they
> > are setting up kdump that they won't get anything out of it?
> 
> Probably a good idea to add something like that.

It will break kdump functionality, it should be fixed instead of
just adding printk to warn user..

Thanks
Dave