diff mbox

[v5,01/40] KVM: arm/arm64: Avoid vcpu_load for other vcpu ioctls than KVM_RUN

Message ID 20180227113429.637-2-cdall@kernel.org (mailing list archive)
State New, archived
Headers show

Commit Message

Christoffer Dall Feb. 27, 2018, 11:33 a.m. UTC 
From: Christoffer Dall <christoffer.dall@linaro.org>

Calling vcpu_load() registers preempt notifiers for this vcpu and calls
kvm_arch_vcpu_load().  The latter will soon be doing a lot of heavy
lifting on arm/arm64 and will try to do things such as enabling the
virtual timer and setting us up to handle interrupts from the timer
hardware.

Loading state onto hardware registers and enabling hardware to signal
interrupts can be problematic when we're not actually about to run the
VCPU, because it makes it difficult to establish the right context when
handling interrupts from the timer, and it makes the register access
code difficult to reason about.

Luckily, now when we call vcpu_load in each ioctl implementation, we can
simply remove the call from the non-KVM_RUN vcpu ioctls, and our
kvm_arch_vcpu_load() is only used for loading vcpu content to the
physical CPU when we're actually going to run the vcpu.

Reviewed-by: Julien Grall <julien.grall@arm.com>
Reviewed-by: Marc Zyngier <marc.zyngier@arm.com>
Reviewed-by: Andrew Jones <drjones@redhat.com>
Signed-off-by: Christoffer Dall <christoffer.dall@linaro.org>
---
 arch/arm64/kvm/guest.c | 3 ---
 virt/kvm/arm/arm.c     | 9 ---------
 2 files changed, 12 deletions(-)

Comments

Marc Zyngier March 7, 2018, 1:01 p.m. UTC | #1 
On 27/02/18 11:33, Christoffer Dall wrote:
> From: Christoffer Dall <christoffer.dall@linaro.org>
> 
> Calling vcpu_load() registers preempt notifiers for this vcpu and calls
> kvm_arch_vcpu_load().  The latter will soon be doing a lot of heavy
> lifting on arm/arm64 and will try to do things such as enabling the
> virtual timer and setting us up to handle interrupts from the timer
> hardware.
> 
> Loading state onto hardware registers and enabling hardware to signal
> interrupts can be problematic when we're not actually about to run the
> VCPU, because it makes it difficult to establish the right context when
> handling interrupts from the timer, and it makes the register access
> code difficult to reason about.
> 
> Luckily, now when we call vcpu_load in each ioctl implementation, we can
> simply remove the call from the non-KVM_RUN vcpu ioctls, and our
> kvm_arch_vcpu_load() is only used for loading vcpu content to the
> physical CPU when we're actually going to run the vcpu.
> 
> Reviewed-by: Julien Grall <julien.grall@arm.com>
> Reviewed-by: Marc Zyngier <marc.zyngier@arm.com>
> Reviewed-by: Andrew Jones <drjones@redhat.com>
> Signed-off-by: Christoffer Dall <christoffer.dall@linaro.org>
I've queued this patch for 4.16-rc5 as part of the reset fix.

Thanks,

	M.
diff mbox

Patch

diff --git a/arch/arm64/kvm/guest.c b/arch/arm64/kvm/guest.c
index d7e3299a7734..959e50d2588c 100644
--- a/arch/arm64/kvm/guest.c
+++ b/arch/arm64/kvm/guest.c
@@ -363,8 +363,6 @@  int kvm_arch_vcpu_ioctl_set_guest_debug(struct kvm_vcpu *vcpu,
 {
 	int ret = 0;
 
-	vcpu_load(vcpu);
-
 	trace_kvm_set_guest_debug(vcpu, dbg->control);
 
 	if (dbg->control & ~KVM_GUESTDBG_VALID_MASK) {
@@ -386,7 +384,6 @@  int kvm_arch_vcpu_ioctl_set_guest_debug(struct kvm_vcpu *vcpu,
 	}
 
 out:
-	vcpu_put(vcpu);
 	return ret;
 }
 
diff --git a/virt/kvm/arm/arm.c b/virt/kvm/arm/arm.c
index 86941f6181bb..53572304843b 100644
--- a/virt/kvm/arm/arm.c
+++ b/virt/kvm/arm/arm.c
@@ -384,14 +384,11 @@  static void vcpu_power_off(struct kvm_vcpu *vcpu)
 int kvm_arch_vcpu_ioctl_get_mpstate(struct kvm_vcpu *vcpu,
 				    struct kvm_mp_state *mp_state)
 {
-	vcpu_load(vcpu);
-
 	if (vcpu->arch.power_off)
 		mp_state->mp_state = KVM_MP_STATE_STOPPED;
 	else
 		mp_state->mp_state = KVM_MP_STATE_RUNNABLE;
 
-	vcpu_put(vcpu);
 	return 0;
 }
 
@@ -400,8 +397,6 @@  int kvm_arch_vcpu_ioctl_set_mpstate(struct kvm_vcpu *vcpu,
 {
 	int ret = 0;
 
-	vcpu_load(vcpu);
-
 	switch (mp_state->mp_state) {
 	case KVM_MP_STATE_RUNNABLE:
 		vcpu->arch.power_off = false;
@@ -413,7 +408,6 @@  int kvm_arch_vcpu_ioctl_set_mpstate(struct kvm_vcpu *vcpu,
 		ret = -EINVAL;
 	}
 
-	vcpu_put(vcpu);
 	return ret;
 }
 
@@ -1036,8 +1030,6 @@  long kvm_arch_vcpu_ioctl(struct file *filp,
 	struct kvm_device_attr attr;
 	long r;
 
-	vcpu_load(vcpu);
-
 	switch (ioctl) {
 	case KVM_ARM_VCPU_INIT: {
 		struct kvm_vcpu_init init;
@@ -1114,7 +1106,6 @@  long kvm_arch_vcpu_ioctl(struct file *filp,
 		r = -EINVAL;
 	}
 
-	vcpu_put(vcpu);
 	return r;
 }