spapr: nested: Add support for DPDES SPR in GSB for TCG L0

The DPDES support for doorbell emulation and handling for KVM on PAPR
guests was added in Linux via [1]. Subsequently, a new GSB (Guest State
Buffer) element for DPDES was added in Linux; the same has been missing
in TCG L0 implementation. Add support for DPDES register's APIv2 GSB
element and required handling in `spapr_nested.c`.

Currently, booting a KVM guest inside a QEMU TCG guest fails with the
following crash. The crash occurs while handling the GUEST_RUN_VCPU
hcall made in TCG L0. In the hcall handling path, map_and_getset_state()
calls getset_state(), which, in turn, calls guest_state_request_check()
to validate the GSR (Guest State Request) elements. During this process,
guest_state_request_check() iterates over the GSR elements and receives
a NULL return code from guest_state_element_type_find() for the type
variable corresponding to the DPDES register's elemetn ID (which was
unknown to TCG L0). Subsequently, getset_state() returns H_P3,
ultimately leading to the hcall failure and causing the KVM guest to
crash.

  KVM: unknown exit, hardware reason ffffffffffffffea
  [ ... KVM register dump ... ]

Fix this by adding the required support in TCG L0 implementation of
APIv2.

[1] https://lore.kernel.org/all/20240605113913.83715-1-gautam@linux.ibm.com/

Fixes: 4a575f9a0567 ("spapr: nested: Initialize the GSB elements lookup table.")
Suggested-by: Harsh Prateek Bora <harshpb@linux.ibm.com>
Signed-off-by: Amit Machhiwal <amachhiw@linux.ibm.com>
Reviewed-by: Harsh Prateek Bora <harshpb@linux.ibm.com>
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>

0 files changed, 0 insertions, 0 deletions