[PATCH] riscv/kvm: Only context-switch senvcfg where it exists

senvcfg arrived in privileged spec 1.12, but H-capable cores on a
1.11 base exist, ie: sifive P500 (ESWIN EIC7700X) implements the
hypervisor extension yet has no senvcfg. KVM swaps the CSR
unconditionally on every vCPU entry, panicing the host upon a guest
executing its first instruction:

  Oops - illegal instruction [#1]
  Modules linked in: kvm
  CPU: 2 UID: 0 PID: 127 Comm: qemu-system-ris Not tainted 7.2.0-kvm73bug+ #4 PREEMPTLAZY
  Hardware name: Unknown Unknown Product/Unknown Product, BIOS 2024.01 01/01/2024
  epc : kvm_riscv_vcpu_enter_exit+0x26/0xcf8 [kvm]
   ra : kvm_arch_vcpu_ioctl_run+0x4ce/0x5a6 [kvm]
  status: 0000000200000100 badaddr: 0000000010a797f3 cause: 0000000000000002
  [<ffffffff01df432e>] kvm_riscv_vcpu_enter_exit+0x26/0xcf8 [kvm]
  [<ffffffff01deb3b0>] kvm_arch_vcpu_ioctl_run+0x4ce/0x5a6 [kvm]
  [<ffffffff01dd7914>] kvm_vcpu_ioctl+0x180/0x5e4 [kvm]
  [<ffffffff8025702e>] __riscv_sys_ioctl+0x84/0x9a
  [<ffffffff80dfdc72>] do_trap_ecall_u+0x1d8/0x38a
  [<ffffffff80e08644>] handle_exception+0x168/0x174
  Code: 84aa 892e b703 8887 1773 1067 3023 16e5 b783 8907 (97f3) 10a7

Touch the CSR only when RISCV_ISA_EXT_XLINUXENVCFG is set, similar
to __switch_to_envcfg() as well as other swaps conditional on
their extentions.

Fixes: db3c01c7a308 ("RISCV: KVM: Add senvcfg context save/restore")
Signed-off-by: Davidlohr Bueso <[email protected]>
---
 arch/riscv/kvm/vcpu.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/arch/riscv/kvm/vcpu.c b/arch/riscv/kvm/vcpu.c
index e062ca19f9d8..0c2d58db13ab 100644
--- a/arch/riscv/kvm/vcpu.c
+++ b/arch/riscv/kvm/vcpu.c
@@ -773,7 +773,8 @@ static __always_inline void kvm_riscv_vcpu_swap_in_guest_state(struct kvm_vcpu *
 	struct kvm_vcpu_csr *csr = &vcpu->arch.guest_csr;
 
 	vcpu->arch.host_scounteren = csr_swap(CSR_SCOUNTEREN, csr->scounteren);
-	vcpu->arch.host_senvcfg = csr_swap(CSR_SENVCFG, csr->senvcfg);
+	if (riscv_has_extension_unlikely(RISCV_ISA_EXT_XLINUXENVCFG))
+		vcpu->arch.host_senvcfg = csr_swap(CSR_SENVCFG, csr->senvcfg);
 	if (riscv_has_extension_unlikely(RISCV_ISA_EXT_SMSTATEEN))
 		vcpu->arch.host_sstateen0 = csr_swap(CSR_SSTATEEN0, smcsr->sstateen0);
 	if (riscv_has_extension_unlikely(RISCV_ISA_EXT_ZICFISS))
@@ -787,7 +788,8 @@ static __always_inline void kvm_riscv_vcpu_swap_in_host_state(struct kvm_vcpu *v
 	struct kvm_vcpu_csr *csr = &vcpu->arch.guest_csr;
 
 	csr->scounteren = csr_swap(CSR_SCOUNTEREN, vcpu->arch.host_scounteren);
-	csr->senvcfg = csr_swap(CSR_SENVCFG, vcpu->arch.host_senvcfg);
+	if (riscv_has_extension_unlikely(RISCV_ISA_EXT_XLINUXENVCFG))
+		csr->senvcfg = csr_swap(CSR_SENVCFG, vcpu->arch.host_senvcfg);
 	if (riscv_has_extension_unlikely(RISCV_ISA_EXT_SMSTATEEN))
 		smcsr->sstateen0 = csr_swap(CSR_SSTATEEN0, vcpu->arch.host_sstateen0);
 	if (riscv_has_extension_unlikely(RISCV_ISA_EXT_ZICFISS))
-- 
2.39.5


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