[Xen-devel] [PATCH V2 0/2] Fix xen crash when starting HVM guest due to missing io handler

[<suravee.suthikulpanit@xxxxxxx>]

From: Suravee Suthikulpanit <Suravee.Suthikulpanit@xxxxxxx>

Hi All,

On systems with iommu v2 enabled, the hypervisor crashes when trying
to start up an HVM guest. 

Investigating shows that the guest_iommu_init() is called before the
HVM domain is initialized. It then tries to register_mmio_handler()
causing the hvm_next_io_handler() to increment the io_handler_count.
However, the registration fails silently and left the I/O handler
uninitialized.

At later time, hvm_find_io_handler() is called and iterate through
the registered handlered, but then resulting in referencing NULL
pointers.

This patch series proposes fix for this issue.

NOTE: For patch 2, since guest IOMMU emulation is still incompleted,
this change is tentative and will be verified in the future. Alterantively,
I can just simply remove the guest_iommu_init()/destroy() for now.
I will be also looking at re-enabling this feature in Xen.

Changes from V1:
  * Fix upper bound NR_IO_HANDLERS check for in patch 1.

Thanks,
Suravee

Suravee Suthikulpanit (2):
  x86/hvm: Add check when register io handler
  svm: iommu: Only call guest_iommu_init() after initialized HVM domain

 xen/arch/x86/hvm/intercept.c                |  6 +++++-
 xen/arch/x86/hvm/svm/svm.c                  | 10 ++++++++++
 xen/drivers/passthrough/amd/iommu_guest.c   |  6 ++++++
 xen/drivers/passthrough/amd/pci_amd_iommu.c |  4 ----
 4 files changed, 21 insertions(+), 5 deletions(-)

-- 
1.9.1


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