linux-kernel - Re: [PATCH v11 0/4] set VSESR_EL2 by user space and support NOTIFY

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Message-ID: <d94439b6-9b9a-9bd0-ddec-3bb63ede9461@arm.com>
Date:   Tue, 10 Apr 2018 15:15:32 +0100
From:   James Morse <james.morse@....com>
To:     Dongjiu Geng <gengdongjiu@...wei.com>
Cc:     rkrcmar@...hat.com, corbet@....net, christoffer.dall@...aro.org,
        marc.zyngier@....com, linux@...linux.org.uk,
        catalin.marinas@....com, rjw@...ysocki.net, bp@...en8.de,
        lenb@...nel.org, kvm@...r.kernel.org, linux-doc@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        kvmarm@...ts.cs.columbia.edu, linux-acpi@...r.kernel.org,
        devel@...ica.org, huangshaoyu@...wei.com, zhengxiang9@...wei.com
Subject: Re: [PATCH v11 0/4] set VSESR_EL2 by user space and support
 NOTIFY_SEI notification

Hi Dongjiu Geng,

On 09/04/18 22:36, Dongjiu Geng wrote:
> 1. Detect whether KVM can set set guest SError syndrome
> 2. Support to Set VSESR_EL2 and inject SError by user space.
> 3. Support live migration to keep SError pending state and VSESR_EL2 value.
> 4. ACPI 6.1 adds support for NOTIFY_SEI as a GHES notification mechanism, so support this
>    notification in software, KVM or kernel ARCH code call handle_guest_sei() to let ACP driver
>    to handle this notification.

Please don't post code during the merge-window, will this apply to v4.17-rc1? We
can't know until its tagged.

This series is doing two separate things, please split it into two series.

But on the ACPI front: I don't see how any OS can support your NOTIFY_SEI when
firmware is ignoring the normal world's PSTATE.A.

The latest lobe of that discussion was on the list here:
https://www.mail-archive.com/linux-kernel@vger.kernel.org/msg1611496.html

As it is, we would need to spot SError being delivered while SError is masked,
spray nasty messages about firmware being horrifically buggy, then panic(). For
a corrected error, this looks bad, but its preferable to letting firmware
silently overwrite the exception registers, causing linux to spin through the
vectors 'eret' with all exceptions masked.
I still think its best to wait for firmware that does the right thing.

Thanks,

James