Re: [PATCH v2 2/2] x86_64: enable SWIOTLB if system has SRAT memory regions above MAX_DMA32_PFN

From: Igor Mammedov
Date: Fri Dec 04 2015 - 07:16:13 EST


On Fri, 4 Dec 2015 12:49:49 +0100
Ingo Molnar <mingo@xxxxxxxxxx> wrote:

>
> * Igor Mammedov <imammedo@xxxxxxxxxx> wrote:
>
> > when memory hotplug enabled system is booted with less
> > than 4GB of RAM and then later more RAM is hotplugged
> > 32-bit devices stop functioning with following error:
> >
> > nommu_map_single: overflow 327b4f8c0+1522 of device mask ffffffff
> >
> > the reason for this is that if x86_64 system were booted
> > with RAM less than 4GB, it doesn't enable SWIOTLB and
> > when memory is hotplugged beyond MAX_DMA32_PFN, devices
> > that expect 32-bit addresses can't handle 64-bit addresses.
> >
> > Fix it by tracking max possible PFN when parsing
> > memory affinity structures from SRAT ACPI table and
> > enable SWIOTLB if there is hotpluggable memory
> > regions beyond MAX_DMA32_PFN.
> >
> > It fixes KVM guests when they use emulated devices
> > (reproduces with ata_piix, e1000 and usb devices,
> > RHBZ: 1275941, 1275977, 1271527)
> > It also fixes the HyperV, VMWare with emulated devices
> > which are affected by this issue as well.
> >
> > Signed-off-by: Igor Mammedov <imammedo@xxxxxxxxxx>
> > ---
> > arch/x86/kernel/pci-swiotlb.c | 2 +-
> > arch/x86/mm/srat.c | 3 +++
> > 2 files changed, 4 insertions(+), 1 deletion(-)
> >
> > diff --git a/arch/x86/kernel/pci-swiotlb.c b/arch/x86/kernel/pci-swiotlb.c
> > index adf0392..7c577a1 100644
> > --- a/arch/x86/kernel/pci-swiotlb.c
> > +++ b/arch/x86/kernel/pci-swiotlb.c
> > @@ -88,7 +88,7 @@ int __init pci_swiotlb_detect_4gb(void)
> > {
> > /* don't initialize swiotlb if iommu=off (no_iommu=1) */
> > #ifdef CONFIG_X86_64
> > - if (!no_iommu && max_pfn > MAX_DMA32_PFN)
> > + if (!no_iommu && max_possible_pfn > MAX_DMA32_PFN)
> > swiotlb = 1;
>
> Ok, this series looks a lot better!
>
> > #endif
> > return swiotlb;
> > diff --git a/arch/x86/mm/srat.c b/arch/x86/mm/srat.c
> > index c2aea63..a26bdbe 100644
> > --- a/arch/x86/mm/srat.c
> > +++ b/arch/x86/mm/srat.c
> > @@ -203,6 +203,9 @@ acpi_numa_memory_affinity_init(struct acpi_srat_mem_affinity *ma)
> > pr_warn("SRAT: Failed to mark hotplug range [mem %#010Lx-%#010Lx] in memblock\n",
> > (unsigned long long)start, (unsigned long long)end - 1);
> >
> > + if (max_possible_pfn < PFN_UP(end - 1))
> > + max_possible_pfn = PFN_UP(end - 1);
>
> Small nit, why not write this as something like:
>
> max_possible_pfn = max(max_possible_pfn, PFN_UP(end - 1));
>
> ?
>
> I'd also move this second hunk to the first patch, because logically it belongs
> there (or into a third patch).
sure, I'll move it to the 1st patch

>
> Thanks,
>
> Ingo

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