Hi,

On Fri, Feb 04, 2022 at 03:40:15PM +0000, Alexandru Elisei wrote:

Hi Marc,

On Fri, Jan 28, 2022 at 12:18:30PM +0000, Marc Zyngier wrote:

quoted

From: Jintack Lim <redacted>

Forward exceptions due to WFI or WFE instructions to the virtual EL2 if
they are not coming from the virtual EL2 and virtual HCR_EL2.TWX is set.

Signed-off-by: Jintack Lim <redacted>
Signed-off-by: Marc Zyngier <maz@kernel.org>
---
 arch/arm64/include/asm/kvm_nested.h |  2 ++
 arch/arm64/kvm/Makefile             |  2 +-
 arch/arm64/kvm/handle_exit.c        | 11 ++++++++++-
 arch/arm64/kvm/nested.c             | 28 ++++++++++++++++++++++++++++
 4 files changed, 41 insertions(+), 2 deletions(-)
 create mode 100644 arch/arm64/kvm/nested.c

diff --git a/arch/arm64/include/asm/kvm_nested.h b/arch/arm64/include/asm/kvm_nested.h
index 5a85be6d8eb3..79d382fa02ea 100644
--- a/arch/arm64/include/asm/kvm_nested.h
+++ b/arch/arm64/include/asm/kvm_nested.h

@@ -65,4 +65,6 @@ static inline u64 translate_cnthctl_el2_to_cntkctl_el1(u64 cnthctl)
 		(cnthctl & (CNTHCTL_EVNTI | CNTHCTL_EVNTDIR | CNTHCTL_EVNTEN)));
 }
 
+int handle_wfx_nested(struct kvm_vcpu *vcpu, bool is_wfe);
+
 #endif /* __ARM64_KVM_NESTED_H */

diff --git a/arch/arm64/kvm/Makefile b/arch/arm64/kvm/Makefile
index b67c4ebd72b1..dbaf42ff65f1 100644
--- a/arch/arm64/kvm/Makefile
+++ b/arch/arm64/kvm/Makefile

@@ -14,7 +14,7 @@ kvm-y += arm.o mmu.o mmio.o psci.o hypercalls.o pvtime.o \
 	 inject_fault.o va_layout.o handle_exit.o \
 	 guest.o debug.o reset.o sys_regs.o \
 	 vgic-sys-reg-v3.o fpsimd.o pmu.o pkvm.o \
-	 arch_timer.o trng.o emulate-nested.o \
+	 arch_timer.o trng.o emulate-nested.o nested.o \
 	 vgic/vgic.o vgic/vgic-init.o \
 	 vgic/vgic-irqfd.o vgic/vgic-v2.o \
 	 vgic/vgic-v3.o vgic/vgic-v4.o \

diff --git a/arch/arm64/kvm/handle_exit.c b/arch/arm64/kvm/handle_exit.c
index 0cedef6e0d80..a1b1bbf3d598 100644
--- a/arch/arm64/kvm/handle_exit.c
+++ b/arch/arm64/kvm/handle_exit.c

@@ -119,7 +119,16 @@ static int handle_no_fpsimd(struct kvm_vcpu *vcpu)
  */
 static int kvm_handle_wfx(struct kvm_vcpu *vcpu)
 {
-	if (kvm_vcpu_get_esr(vcpu) & ESR_ELx_WFx_ISS_WFE) {
+	bool is_wfe = !!(kvm_vcpu_get_esr(vcpu) & ESR_ELx_WFx_ISS_WFE);
+
+	if (vcpu_has_nv(vcpu)) {
+		int ret = handle_wfx_nested(vcpu, is_wfe);
+
+		if (ret != -EINVAL)
+			return ret;

I find this rather clunky. The common pattern is that a function returns
early when it encounters an error, but here this pattern is reversed:
-EINVAL means that handle_wfx_nested() failed in handling the WFx, so
proceed as usual; conversly, anything but -EINVAL means handle_wfx_nested()
was successful in handling WFx, so exit early from kvm_handle_wfx().

That would be ok by itself, but if we dig deeper, handle_wfx_nested() ends up
calling kvm_inject_nested(), where -EINVAL is actually an error code. Granted,
that should never happen, because kvm_handle_wfx() first checks vcpu_has_nv(),
but still feels like something that could be improved.

Maybe changing handle_wfx_nested() like this would be better:
[..]

Or change kvm_handle_wfx() to handle the WFx trap like kvm_handle_fpasimd():

	if (guest_wfx_traps_enabled(vcpu))
		return kvm_inject_nested_sync(vcpu, kvm_vcpu_get_esr(vcpu));

Thanks,
Alex

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