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Re: [PATCH RFC 0/6] i386/pc: Fix creation of >= 1Tb guests on AMD system
From: |
David Edmondson |
Subject: |
Re: [PATCH RFC 0/6] i386/pc: Fix creation of >= 1Tb guests on AMD systems with IOMMU |
Date: |
Wed, 23 Jun 2021 08:40:56 +0100 |
On Tuesday, 2021-06-22 at 15:16:29 -06, Alex Williamson wrote:
>> Additionally, an alternative to hardcoded ranges as we do today,
>> VFIO could advertise the platform valid IOVA ranges without
>> necessarily
>> requiring to have a PCI device added in the vfio container. That
>> would
>> fetching the valid IOVA ranges from VFIO, rather than hardcoded IOVA
>> ranges as we do today. But sadly, wouldn't work for older
>> hypervisors.
>
>
> $ grep -h . /sys/kernel/iommu_groups/*/reserved_regions | sort -u
> 0x00000000fee00000 0x00000000feefffff msi
> 0x000000fd00000000 0x000000ffffffffff reserved
>
> Ideally we might take that into account on all hosts, but of course
> then we run into massive compatibility issues when we consider
> migration. We run into similar problems when people try to assign
> devices to non-x86 TCG hosts, where the arch doesn't have a natural
> memory hole overlapping the msi range.
>
> The issue here is similar to trying to find a set of supported CPU
> flags across hosts, QEMU only has visibility to the host where it runs,
> an upper level tool needs to be able to pass through information about
> compatibility to all possible migration targets. Towards that end, we
> should probably have command line options that either allow to specify
> specific usable or reserved GPA address ranges. For example something
> like:
> --reserved-mem-ranges=host
>
> Or explicitly:
>
> --reserved-mem-ranges=13G@1010G,1M@4078M
Would this not naturally be a property of a machine model?
dme.
--
Seems I'm not alone at being alone.
- [PATCH RFC 3/6] pc/cmos: Adjust CMOS above 4G memory size according to 1Tb boundary, (continued)
- [PATCH RFC 3/6] pc/cmos: Adjust CMOS above 4G memory size according to 1Tb boundary, Joao Martins, 2021/06/22
- [PATCH RFC 4/6] i386/pc: Keep PCI 64-bit hole within usable IOVA space, Joao Martins, 2021/06/22
- [PATCH RFC 5/6] i386/acpi: Fix SRAT ranges in accordance to usable IOVA, Joao Martins, 2021/06/22
- [PATCH RFC 6/6] i386/pc: Add a machine property for AMD-only enforcing of valid IOVAs, Joao Martins, 2021/06/22
- Re: [PATCH RFC 0/6] i386/pc: Fix creation of >= 1Tb guests on AMD systems with IOMMU, Alex Williamson, 2021/06/22