linux-kernel - Re: [PATCH 0/5] iommu/amd: fixes for suspend/resume

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Message-ID: <44f3f76cb14bafee2d81a615f258a4fb4be93fe1.camel@redhat.com>
Date:   Thu, 02 Dec 2021 01:08:01 +0200
From:   Maxim Levitsky <mlevitsk@...hat.com>
To:     linux-kernel@...r.kernel.org
Cc:     David Woodhouse <dwmw@...zon.co.uk>,
        Suravee Suthikulpanit <suravee.suthikulpanit@....com>,
        Joerg Roedel <joro@...tes.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        "open list:AMD IOMMU (AMD-VI)" <iommu@...ts.linux-foundation.org>,
        Will Deacon <will@...nel.org>
Subject: Re: [PATCH 0/5] iommu/amd: fixes for suspend/resume

On Tue, 2021-11-23 at 18:10 +0200, Maxim Levitsky wrote:
> As I sadly found out, a s3 cycle makes the AMD's iommu stop sending interrupts
> until the system is rebooted.
> 
> I only noticed it now because otherwise the IOMMU works, and these interrupts
> are only used for errors and for GA log which I tend not to use by
> making my VMs do mwait/pause/etc in guest (cpu-pm=on).
> 
> There are two issues here that prevent interrupts from being generated after
> s3 cycle:
> 
> 1. GA log base address was not restored after resume, and was all zeroed
> after resume (by BIOS or such).
> 
> In theory if BIOS writes some junk to it, that can even cause a memory corruption.
> Patch 2 fixes that.
> 
> 2. INTX (aka x2apic mode) settings were not restored after resume.
> That mode is used regardless if the host uses/supports x2apic, but rather when
> the IOMMU supports it, and mine does.
> Patches 3-4 fix that.
> 
> Note that there is still one slight (userspace) bug remaining:
> During suspend all but the boot CPU are offlined and then after resume
> are onlined again.
> 
> The offlining moves all non-affinity managed interrupts to CPU0, and
> later when all other CPUs are onlined, there is nothing in the kernel
> to spread back the interrupts over the cores.
> 
> The userspace 'irqbalance' daemon does fix this but it seems to ignore
> the IOMMU interrupts in INTX mode since they are not attached to any
> PCI device, and thus they remain on CPU0 after a s3 cycle,
> which is suboptimal when the system has multiple IOMMUs
> (mine has 4 of them).
> 
> Setting the IRQ affinity manually via /proc/irq/ does work.
> 
> This was tested on my 3970X with both INTX and regular MSI mode (later was enabled
> by patching out INTX detection), by running a guest with AVIC enabled and with
> a PCI assigned device (network card), and observing interrupts from
> IOMMU while guest is mostly idle.
> 
> This was also tested on my AMD laptop with 4650U (which has the same issue)
> (I tested only INTX mode)
> 
> Patch 1 is a small refactoring to remove an unused struct field.
> 
> Best regards,
>    Maxim Levitsky
> 
> Maxim Levitsky (5):
>   iommu/amd: restore GA log/tail pointer on host resume
>   iommu/amd: x2apic mode: re-enable after resume
>   iommu/amd: x2apic mode: setup the INTX registers on mask/unmask
>   iommu/amd: x2apic mode: mask/unmask interrupts on suspend/resume
>   iommu/amd: remove useless irq affinity notifier
> 
>  drivers/iommu/amd/amd_iommu_types.h |   2 -
>  drivers/iommu/amd/init.c            | 107 +++++++++++++++-------------
>  2 files changed, 58 insertions(+), 51 deletions(-)
> 
> -- 
> 2.26.3
> 
> 

Polite ping on these patches.
Best regards,
	Maxim Levitsky