linux-kernel - Re: [PATCH 00/10] GICv3 support for kexec/kdump on EFI systems

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Date:   Fri, 28 Sep 2018 11:33:48 +0100
From:   Marc Zyngier <marc.zyngier@....com>
To:     Richard Ruigrok <rruigrok@...eaurora.org>,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org
Cc:     Jeffrey Hugo <jhugo@...eaurora.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Jason Cooper <jason@...edaemon.net>,
        Jeremy Linton <jeremy.linton@....com>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>
Subject: Re: [PATCH 00/10] GICv3 support for kexec/kdump on EFI systems

Hi Richard,

On 27/09/18 22:10, Richard Ruigrok wrote:
> Hi Marc
> 
> On 9/21/2018 1:59 PM, Marc Zyngier wrote:
>> The GICv3 architecture has the remarkable feature that once LPI tables
>> have been assigned to redistributors and that LPI delivery is enabled,
>> there is no guarantee that LPIs can be turned off (and most
>> implementations do not allow it), nor can it be reprogrammed to use
>> other tables.
>>
>> This is a bit of a problem for kexec, where the secondary kernel
>> completely looses track of the previous allocations. If the secondary
>> kernel doesn't allocate the tables exactly the same way, no LPIs will
>> be delivered by the GIC (which continues to use the old tables), and
>> memory previously allocated for the pending tables will be slowly
>> corrupted, one bit at a time.
>>
>> The workaround for this is based on a series[1] by Ard Biesheuvel,
>> which adds the required infrastructure for memory reservations to be
>> passed from one kernel to another using an EFI table.
>>
>> This infrastructure is then used to register the allocation of GIC
>> tables with EFI, and allow the GIC driver to safely reuse the existing
>> programming if it detects that the tables have been correctly
>> registered. On non-EFI systems, there is not much we can do.
>>
>> This has been tested on a TX2 system both as a host and a guest. I'd
>> welcome additional testing of different HW. For convenience, I've
>> stashed a branch containing the whole thing at [2].
> I tested [2] from the 4.19-rc4 set which included this series and [1].
> Tested kexec on Centriq system with ITS support (46 core).  On-board was a MLX CX5 NIC, verified MSIs are active in /proc/interrupts.
> Prior to this we used a workaround from Shanker to reuse the same tables in the kexec'ed kernel.

Yes, I remember seeing this workaround. Hopefully we're in a better 
place now that we can guarantee that the tables are not reused.

> Let me know if further testing is needed, and thanks for adding this support.

Good to know, thanks for having tested it. I've now put this code into 
-next for some more soaking. Hopefully nothing horrible will happen ;-)

	M.
-- 
Jazz is not dead. It just smells funny...