KVM: PPC: Book3S HV: Add preempt_disable() around virtual-mode HPTE bit-lock users

kvmppc_hv_find_lock_hpte() requires virtual-mode callers to run with
preemption disabled, because it can return with HPTE_V_HVLOCK still held
until the caller later unlocks the HPTE.  Existing virtual-mode callers
in book3s_64_mmu_hv.c already follow that rule.

Two virtual-mode call paths do not:

1. kvmppc_handle_exit_hv() calls kvmppc_hpte_hv_fault() for hash-mode
   data-side and instruction-side faults after guest exit, with
   preemption already enabled.  kvmppc_hpte_hv_fault() calls
   kvmppc_hv_find_lock_hpte() directly.

2. kvmppc_pseries_do_hcall() executes virtual-mode handlers for HPT
   hcalls via kvmppc_pseries_do_hpt_hcall() with preemption enabled.
   The handlers for H_ENTER, H_REMOVE, H_READ, H_CLEAR_MOD, H_CLEAR_REF,
   H_PROTECT, and H_BULK_REMOVE spin on try_lock_hpte() or lock_rmap(),
   and H_ENTER also reaches kvmppc_do_h_enter(), which uses
   arch_spin_lock() on kvm->mmu_lock.  That raw lock choice is
   intentional because kvmppc_do_h_enter() is also used by real-mode
   callers, so the correct fix is to establish the proper preemption
   context at the virtual-mode caller boundary.

If a vCPU thread is preempted while holding HPTE_V_HVLOCK, any other
thread on the same CPU trying to acquire the same bit-lock can spin
indefinitely.  The same applies to lock_rmap() users and to the H_ENTER
path while holding the raw mmu_lock.

Fix this by adding preempt_disable()/preempt_enable() pairs around the
two kvmppc_hpte_hv_fault() call sites in kvmppc_handle_exit_hv(), and
around the kvmppc_pseries_do_hpt_hcall() invocation in
kvmppc_pseries_do_hcall().  Targeting only the HPT hcall helper avoids
wrapping non-HPT hcalls (such as H_RTAS, H_CONFER, H_REGISTER_VPA) that
perform page faults, blocking memory allocations, or context switches.

Fixes: 6165d5dd99db ("KVM: PPC: Book3S HV: add virtual mode handlers for HPT hcalls and page faults")
Cc: stable@vger.kernel.org # v5.14+
Signed-off-by: Amit Machhiwal <amachhiw@linux.ibm.com>
Reviewed-by: Ritesh Harjani (IBM) <ritesh.list@gmail.com>
Signed-off-by: Madhavan Srinivasan <maddy@linux.ibm.com>
Link: https://patch.msgid.link/20260928122837.8782-3-amachhiw@linux.ibm.com

0 files changed, 0 insertions, 0 deletions