Commit b8f8d190 authored by Marc Zyngier's avatar Marc Zyngier
Browse files

KVM: arm64: Document the behaviour of S1PTW faults on RO memslots 



Although the KVM API says that a write to a RO memslot must result
in a KVM_EXIT_MMIO describing the write, the arm64 architecture
doesn't provide the *data* written by a Stage-1 page table walk
(we only get the address).

Since there isn't much userspace can do with so little information
anyway, document the fact that such an access results in a guest
exception, not an exit. This is consistent with the guest being
terminally broken anyway.

Reviewed-by: default avatarOliver Upton <oliver.upton@linux.dev>
Signed-off-by: default avatarMarc Zyngier <maz@kernel.org>
parent 406504c7

Documentation/virt/kvm/api.rst

+8 −0
Original line number Diff line number Diff line
@@ -1354,6 +1354,14 @@ the memory region are automatically reflected into the guest. For example, an 
mmap() that affects the region will be made visible immediately.  Another

example is madvise(MADV_DROP).



Note: On arm64, a write generated by the page-table walker (to update

the Access and Dirty flags, for example) never results in a

KVM_EXIT_MMIO exit when the slot has the KVM_MEM_READONLY flag. This

is because KVM cannot provide the data that would be written by the

page-table walker, making it impossible to emulate the access.

Instead, an abort (data abort if the cause of the page-table update

was a load or a store, instruction abort if it was an instruction

fetch) is injected in the guest.



4.36 KVM_SET_TSS_ADDR

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