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[RFC,0/2] arm: Add DMA remapping for CCA

Message ID 20250220161320.518450-2-jean-philippe@linaro.org
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Series arm: Add DMA remapping for CCA | expand

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Jean-Philippe Brucker Feb. 20, 2025, 4:13 p.m. UTC 
These two patches will be included in the series that adds support for
Arm CCA guests to QEMU, which isn't ready to be merged [1], but I'm sending
them as RFC first to seek advice about the best way to implement this.

There is a breaking change to CCA guests, where DMA addresses now have
the "shared" top bit set. The VMM needs to strip the address before
accessing memory. See more details on patch 2 of this RFC and on the
Linux change:

https://lore.kernel.org/all/20250219220751.1276854-1-suzuki.poulose@arm.com/

Patch 2 inserts an IOMMUMemoryRegion on the DMA path, so all DMA
accesses get the top bit stripped. It also adds RAM discard listeners
(guest_memfd -> IOMMU notifiers) so that we can create VFIO mappings in
the top half of the guest address space. Patch 1 is a hack to support
GPA->VA translation during the discard_populate notification.

I'm testing VFIO support using Chenyi Qiang's series for shared device
assignment [2]

[1] https://lore.kernel.org/qemu-devel/20241125195626.856992-2-jean-philippe@linaro.org/
[2] https://lore.kernel.org/qemu-devel/20250217081833.21568-1-chenyi.qiang@intel.com/

Jean-Philippe Brucker (2):
  system/memory: Allow creating IOMMU mappings from RAM discard populate
    notifiers
  target/arm/kvm-rme: Add DMA remapping for the shared memory region

 include/exec/memory.h |   5 +
 target/arm/kvm_arm.h  |  15 +++
 hw/arm/virt.c         |   2 +
 system/memory.c       |   3 +-
 target/arm/kvm-rme.c  | 220 ++++++++++++++++++++++++++++++++++++++++++
 5 files changed, 244 insertions(+), 1 deletion(-)