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

Maxim Levitsky
2021-12-01T23:08:17Z

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