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Re: [RFC v2 1/1] memory: Delete assertion in memory_region_unregister_io
From: |
Peter Xu |
Subject: |
Re: [RFC v2 1/1] memory: Delete assertion in memory_region_unregister_iommu_notifier |
Date: |
Tue, 30 Jun 2020 11:39:11 -0400 |
On Tue, Jun 30, 2020 at 10:41:10AM +0800, Jason Wang wrote:
> > /* According to ATS spec table 2.4:
> > * S = 0, bits 15:12 = xxxx range size: 4K
> > * S = 1, bits 15:12 = xxx0 range size: 8K
> > * S = 1, bits 15:12 = xx01 range size: 16K
> > * S = 1, bits 15:12 = x011 range size: 32K
> > * S = 1, bits 15:12 = 0111 range size: 64K
> > * ...
> > */
>
>
> Right, but the comment is probably misleading here, since it's for the PCI-E
> transaction between IOMMU and device not for the device IOTLB invalidation
> descriptor.
>
> For device IOTLB invalidation descriptor, spec allows a [0, ~0ULL]
> invalidation:
>
> "
>
> 6.5.2.5 Device-TLB Invalidate Descriptor
>
> ...
>
> Size (S): The size field indicates the number of consecutive pages targeted
> by this invalidation
> request. If S field is zero, a single page at page address specified by
> Address [63:12] is requested
> to be invalidated. If S field is Set, the least significant bit in the
> Address field with value 0b
> indicates the invalidation address range. For example, if S field is Set and
> Address[12] is Clear, it
> indicates an 8KB invalidation address range with base address in Address
> [63:13]. If S field and
> Address[12] is Set and bit 13 is Clear, it indicates a 16KB invalidation
> address range with base
> address in Address [63:14], etc.
>
> "
>
> So if we receive an address whose [63] is 0 and the rest is all 1, it's then
> a [0, ~0ULL] invalidation.
Yes. I think invalidating the whole range is always fine. It's still not
arbitrary, right? E.g., we can't even invalidate (0x1000, 0x3000) with
device-iotlb because of the address mask, not to say sub-pages.
>
>
> >
> > >
> > > > > How about just convert to use a range [start, end] for any notifier
> > > > > and move
> > > > > the checks (e.g the assert) into the actual notifier implemented
> > > > > (vhost or
> > > > > vfio)?
> > > > IOMMUTLBEntry itself is the abstraction layer of TLB entry. Hardware
> > > > TLB entry
> > > > is definitely not arbitrary range either (because AFAICT the hardware
> > > > should
> > > > only cache PFN rather than address, so at least PAGE_SIZE aligned).
> > > > Introducing this flag will already make this trickier just to avoid
> > > > introducing
> > > > another similar struct to IOMMUTLBEntry, but I really don't want to
> > > > make it a
> > > > default option... Not to mention I probably have no reason to urge the
> > > > rest
> > > > iommu notifier users (tcg, vfio) to change their existing good code to
> > > > suite
> > > > any of the backend who can cooperate with arbitrary address ranges...
> > >
> > > Ok, so it looks like we need a dedicated notifiers to device IOTLB.
> > Or we can also make a new flag for device iotlb just like current UNMAP?
> > Then
> > we replace the vhost type from UNMAP to DEVICE_IOTLB. But IMHO using the
> > ARBITRARY_LENGTH flag would work in a similar way. DEVICE_IOTLB flag could
> > also allow virtio/vhost to only receive one invalidation (now IIUC it'll
> > receive both iotlb and device-iotlb for unmapping a page when ats=on), but
> > then
> > ats=on will be a must and it could break some old (misconfiged) qemu because
> > afaict previously virtio/vhost could even work with vIOMMU (accidentally)
> > even
> > without ats=on.
>
>
> That's a bug and I don't think we need to workaround mis-configurated qemu
> :)
IMHO it depends on the strictness we want on the qemu cmdline API. :)
We should at least check libvirt to make sure it's using ats=on always, then I
agree maybe we can avoid considering the rest...
Thanks,
--
Peter Xu
- Re: [RFC v2 1/1] memory: Delete assertion in memory_region_unregister_iommu_notifier, (continued)
- Re: [RFC v2 1/1] memory: Delete assertion in memory_region_unregister_iommu_notifier, Yan Zhao, 2020/06/27
- Re: [RFC v2 1/1] memory: Delete assertion in memory_region_unregister_iommu_notifier, Jason Wang, 2020/06/28
- Re: [RFC v2 1/1] memory: Delete assertion in memory_region_unregister_iommu_notifier, Peter Xu, 2020/06/28
- Re: [RFC v2 1/1] memory: Delete assertion in memory_region_unregister_iommu_notifier, Jason Wang, 2020/06/29
- Re: [RFC v2 1/1] memory: Delete assertion in memory_region_unregister_iommu_notifier, Peter Xu, 2020/06/29
- Re: [RFC v2 1/1] memory: Delete assertion in memory_region_unregister_iommu_notifier, Jason Wang, 2020/06/29
- Re: [RFC v2 1/1] memory: Delete assertion in memory_region_unregister_iommu_notifier, Jason Wang, 2020/06/30
- Re: [RFC v2 1/1] memory: Delete assertion in memory_region_unregister_iommu_notifier, Michael S. Tsirkin, 2020/06/30
- Re: [RFC v2 1/1] memory: Delete assertion in memory_region_unregister_iommu_notifier, Jason Wang, 2020/06/30
- Re: [RFC v2 1/1] memory: Delete assertion in memory_region_unregister_iommu_notifier, Peter Xu, 2020/06/30
- Re: [RFC v2 1/1] memory: Delete assertion in memory_region_unregister_iommu_notifier,
Peter Xu <=
Re: [RFC v2 0/1] memory: Delete assertion in memory_region_unregister_iommu_notifier, Paolo Bonzini, 2020/06/29