[RFC PATCH 10/12] RISC-V: KVM: Accept auto-mode interrupt files for IMSIC IRQ bypass

[Gong Shuai]

The IRQ bypass required the AIA to be in HWACCEL mode, while the KVM
default is AUTO, which publishes an IMSIC VS-file whenever one is
available and only falls back to the SW-file when the host has none
left. Rejecting AUTO leaves every assigned device on host MSI delivery,
which cannot work for a device attached to a nested domain because its
stage-1 page tables belong to the guest, so the device keeps the host
MSI address composed at vector activation and its MSIs fault in the
guest stage-1.

Co-developed-by: Wu Fei <wu.fei9 at sanechips.com.cn>
Signed-off-by: Wu Fei <wu.fei9 at sanechips.com.cn>
Signed-off-by: Gong Shuai <gong.shuai at sanechips.com.cn>
---
 arch/riscv/kvm/aia_imsic.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/arch/riscv/kvm/aia_imsic.c b/arch/riscv/kvm/aia_imsic.c
index 37e27f28dc62..010f9a90f107 100644
--- a/arch/riscv/kvm/aia_imsic.c
+++ b/arch/riscv/kvm/aia_imsic.c
@@ -981,10 +981,13 @@ static int imsic_irqfd_forward(struct kvm_kernel_irqfd *irqfd,
 	 * MSI-X because pci_write_msi_msg() masks an MSI-X vector around the
 	 * update, which conventional MSI cannot provide.
 	 */
-	if (kvm->arch.aia.mode != KVM_DEV_RISCV_AIA_MODE_HWACCEL ||
-	    !imsic_irqfd_is_msix(irqfd))
+	if (!imsic_irqfd_is_msix(irqfd))
 		return -EOPNOTSUPP;
 
+	/*
+	 * The IOMMU writes MSIs straight into the VS-file, so bypass is
+	 * gated by the hardware backing checks below, not the AIA mode.
+	 */
 	if (!imsic_targets_valid(&kvm->arch.aia)) {
 		pr_debug("KVM: IMSIC IRQ bypass requires all VS-files\n");
 		return -EOPNOTSUPP;
-- 
2.53.0