[PATCH v3 0/3] KVM: arm64: Use generic guest entry infrastructure

[PATCH v3 0/3] KVM: arm64: Use generic guest entry infrastructure

[Oliver Upton]

The arm64 kernel doesn't yet support the full generic entry
infrastructure. That being said, KVM/arm64 doesn't properly handle
TIF_NOTIFY_RESUME and could pick this up by switching to the generic
guest entry infrasturture.

Patch 1 adds a missing vCPU stat to ARM64 to record the number of signal
exits to userspace.

Patch 2 unhitches entry-kvm from entry-generic, as ARM64 doesn't
currently support the generic infrastructure.

Patch 3 replaces the open-coded entry handling with the generic xfer
function.

This series was tested on an Ampere Mt. Jade reference system. The
series cleanly applies to kvm/queue (note that this is deliberate as the
generic kvm stats patches have not yet propagated to kvm-arm/queue) at
the following commit:

8ad5e63649ff ("KVM: Don't take mmu_lock for range invalidation unless necessary")

v1 -> v2:
 - Address Jing's comment
 - Carry Jing's r-b tag

v2 -> v3:
 - Roll all exit conditions into kvm_vcpu_exit_request() (Marc)
 - Avoid needlessly checking for work twice (Marc)

v1: http://lore.kernel.org/r/20210729195632.489978-1-oupton@google.com
v2: http://lore.kernel.org/r/20210729220916.1672875-1-oupton@google.com

Oliver Upton (3):
  KVM: arm64: Record number of signal exits as a vCPU stat
  entry: KVM: Allow use of generic KVM entry w/o full generic support
  KVM: arm64: Use generic KVM xfer to guest work function

 arch/arm64/include/asm/kvm_host.h |  1 +
 arch/arm64/kvm/Kconfig            |  1 +
 arch/arm64/kvm/arm.c              | 71 +++++++++++++++++++------------
 arch/arm64/kvm/guest.c            |  1 +
 include/linux/entry-kvm.h         |  6 ++-
 5 files changed, 52 insertions(+), 28 deletions(-)

-- 
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[PATCH v3 1/3] KVM: arm64: Record number of signal exits as a vCPU stat

[Oliver Upton]

Most other architectures that implement KVM record a statistic
indicating the number of times a vCPU has exited due to a pending
signal. Add support for that stat to arm64.

Reviewed-by: Jing Zhang <jingzhangos@google.com>
Signed-off-by: Oliver Upton <oupton@google.com>
---
 arch/arm64/include/asm/kvm_host.h | 1 +
 arch/arm64/kvm/arm.c              | 1 +
 arch/arm64/kvm/guest.c            | 1 +
 3 files changed, 3 insertions(+)

diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
index 41911585ae0c..70e129f2b574 100644
--- a/arch/arm64/include/asm/kvm_host.h
+++ b/arch/arm64/include/asm/kvm_host.h
@@ -576,6 +576,7 @@ struct kvm_vcpu_stat {
 	u64 wfi_exit_stat;
 	u64 mmio_exit_user;
 	u64 mmio_exit_kernel;
+	u64 signal_exits;
 	u64 exits;
 };
 
diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c
index e9a2b8f27792..60d0a546d7fd 100644
--- a/arch/arm64/kvm/arm.c
+++ b/arch/arm64/kvm/arm.c
@@ -783,6 +783,7 @@ int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu)
 		if (signal_pending(current)) {
 			ret = -EINTR;
 			run->exit_reason = KVM_EXIT_INTR;
+			++vcpu->stat.signal_exits;
 		}
 
 		/*
diff --git a/arch/arm64/kvm/guest.c b/arch/arm64/kvm/guest.c
index 1dfb83578277..853d1e8d2e73 100644
--- a/arch/arm64/kvm/guest.c
+++ b/arch/arm64/kvm/guest.c
@@ -50,6 +50,7 @@ const struct _kvm_stats_desc kvm_vcpu_stats_desc[] = {
 	STATS_DESC_COUNTER(VCPU, wfi_exit_stat),
 	STATS_DESC_COUNTER(VCPU, mmio_exit_user),
 	STATS_DESC_COUNTER(VCPU, mmio_exit_kernel),
+	STATS_DESC_COUNTER(VCPU, signal_exits),
 	STATS_DESC_COUNTER(VCPU, exits)
 };
 static_assert(ARRAY_SIZE(kvm_vcpu_stats_desc) ==
-- 
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[PATCH v3 2/3] entry: KVM: Allow use of generic KVM entry w/o full generic support

[Oliver Upton]

Some architectures (e.g. arm64) have yet to adopt the generic entry
infrastructure. Despite that, it would be nice to use some common
plumbing for guest entry/exit handling. For example, KVM/arm64 currently
does not handle TIF_NOTIFY_PENDING correctly.

Allow use of only the generic KVM entry code by tightening up the
include list. No functional change intended.

Signed-off-by: Oliver Upton <oupton@google.com>
---
 include/linux/entry-kvm.h | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/include/linux/entry-kvm.h b/include/linux/entry-kvm.h
index 136b8d97d8c0..0d7865a0731c 100644
--- a/include/linux/entry-kvm.h
+++ b/include/linux/entry-kvm.h
@@ -2,7 +2,11 @@
 #ifndef __LINUX_ENTRYKVM_H
 #define __LINUX_ENTRYKVM_H
 
-#include <linux/entry-common.h>
+#include <linux/static_call_types.h>
+#include <linux/tracehook.h>
+#include <linux/syscalls.h>
+#include <linux/seccomp.h>
+#include <linux/sched.h>
 #include <linux/tick.h>
 
 /* Transfer to guest mode work */
-- 
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[PATCH v3 3/3] KVM: arm64: Use generic KVM xfer to guest work function

[Oliver Upton]

Clean up handling of checks for pending work by switching to the generic
infrastructure to do so.

We pick up handling for TIF_NOTIFY_RESUME from this switch, meaning that
task work will be correctly handled.

Signed-off-by: Oliver Upton <oupton@google.com>
---
 arch/arm64/kvm/Kconfig |  1 +
 arch/arm64/kvm/arm.c   | 72 ++++++++++++++++++++++++++----------------
 2 files changed, 45 insertions(+), 28 deletions(-)

diff --git a/arch/arm64/kvm/Kconfig b/arch/arm64/kvm/Kconfig
index a4eba0908bfa..8bc1fac5fa26 100644
--- a/arch/arm64/kvm/Kconfig
+++ b/arch/arm64/kvm/Kconfig
@@ -26,6 +26,7 @@ menuconfig KVM
 	select HAVE_KVM_ARCH_TLB_FLUSH_ALL
 	select KVM_MMIO
 	select KVM_GENERIC_DIRTYLOG_READ_PROTECT
+	select KVM_XFER_TO_GUEST_WORK
 	select SRCU
 	select KVM_VFIO
 	select HAVE_KVM_EVENTFD
diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c
index 60d0a546d7fd..8245efc6e88f 100644
--- a/arch/arm64/kvm/arm.c
+++ b/arch/arm64/kvm/arm.c
@@ -6,6 +6,7 @@
 
 #include <linux/bug.h>
 #include <linux/cpu_pm.h>
+#include <linux/entry-kvm.h>
 #include <linux/errno.h>
 #include <linux/err.h>
 #include <linux/kvm_host.h>
@@ -714,6 +715,45 @@ static bool vcpu_mode_is_bad_32bit(struct kvm_vcpu *vcpu)
 		static_branch_unlikely(&arm64_mismatched_32bit_el0);
 }
 
+/**
+ * kvm_vcpu_exit_request - returns true if the VCPU should *not* enter the guest
+ * @vcpu:	The VCPU pointer
+ * @ret:	Pointer to write optional return code
+ *
+ * Returns: true if the VCPU needs to return to a preemptible + interruptible
+ *	    and skip guest entry.
+ *
+ * This function disambiguates between two different types of exits: exits to a
+ * preemptible + interruptible kernel context and exits to userspace. For an
+ * exit to userspace, this function will write the return code to ret and return
+ * true. For an exit to preemptible + interruptible kernel context (i.e. check
+ * for pending work and re-enter), return true without writing to ret.
+ */
+static bool kvm_vcpu_exit_request(struct kvm_vcpu *vcpu, int *ret)
+{
+	struct kvm_run *run = vcpu->run;
+
+	/*
+	 * If we're using a userspace irqchip, then check if we need
+	 * to tell a userspace irqchip about timer or PMU level
+	 * changes and if so, exit to userspace (the actual level
+	 * state gets updated in kvm_timer_update_run and
+	 * kvm_pmu_update_run below).
+	 */
+	if (static_branch_unlikely(&userspace_irqchip_in_use)) {
+		if (kvm_timer_should_notify_user(vcpu) ||
+		    kvm_pmu_should_notify_user(vcpu)) {
+			*ret = -EINTR;
+			run->exit_reason = KVM_EXIT_INTR;
+			return true;
+		}
+	}
+
+	return kvm_request_pending(vcpu) ||
+			need_new_vmid_gen(&vcpu->arch.hw_mmu->vmid) ||
+			xfer_to_guest_mode_work_pending();
+}
+
 /**
  * kvm_arch_vcpu_ioctl_run - the main VCPU run function to execute guest code
  * @vcpu:	The VCPU pointer
@@ -757,7 +797,9 @@ int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu)
 		/*
 		 * Check conditions before entering the guest
 		 */
-		cond_resched();
+		ret = xfer_to_guest_mode_handle_work(vcpu);
+		if (!ret)
+			ret = 1;
 
 		update_vmid(&vcpu->arch.hw_mmu->vmid);
 
@@ -776,31 +818,6 @@ int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu)
 
 		kvm_vgic_flush_hwstate(vcpu);
 
-		/*
-		 * Exit if we have a signal pending so that we can deliver the
-		 * signal to user space.
-		 */
-		if (signal_pending(current)) {
-			ret = -EINTR;
-			run->exit_reason = KVM_EXIT_INTR;
-			++vcpu->stat.signal_exits;
-		}
-
-		/*
-		 * If we're using a userspace irqchip, then check if we need
-		 * to tell a userspace irqchip about timer or PMU level
-		 * changes and if so, exit to userspace (the actual level
-		 * state gets updated in kvm_timer_update_run and
-		 * kvm_pmu_update_run below).
-		 */
-		if (static_branch_unlikely(&userspace_irqchip_in_use)) {
-			if (kvm_timer_should_notify_user(vcpu) ||
-			    kvm_pmu_should_notify_user(vcpu)) {
-				ret = -EINTR;
-				run->exit_reason = KVM_EXIT_INTR;
-			}
-		}
-
 		/*
 		 * Ensure we set mode to IN_GUEST_MODE after we disable
 		 * interrupts and before the final VCPU requests check.
@@ -809,8 +826,7 @@ int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu)
 		 */
 		smp_store_mb(vcpu->mode, IN_GUEST_MODE);
 
-		if (ret <= 0 || need_new_vmid_gen(&vcpu->arch.hw_mmu->vmid) ||
-		    kvm_request_pending(vcpu)) {
+		if (ret <= 0 || kvm_vcpu_exit_request(vcpu, &ret)) {
 			vcpu->mode = OUTSIDE_GUEST_MODE;
 			isb(); /* Ensure work in x_flush_hwstate is committed */
 			kvm_pmu_sync_hwstate(vcpu);
-- 
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Re: [PATCH v3 0/3] KVM: arm64: Use generic guest entry infrastructure

[Oliver Upton]

Friendly ping :)

--
Thanks,
Oliver

On Mon, Aug 2, 2021 at 12:28 PM Oliver Upton <oupton@google.com> wrote:
>
> The arm64 kernel doesn't yet support the full generic entry
> infrastructure. That being said, KVM/arm64 doesn't properly handle
> TIF_NOTIFY_RESUME and could pick this up by switching to the generic
> guest entry infrasturture.
>
> Patch 1 adds a missing vCPU stat to ARM64 to record the number of signal
> exits to userspace.
>
> Patch 2 unhitches entry-kvm from entry-generic, as ARM64 doesn't
> currently support the generic infrastructure.
>
> Patch 3 replaces the open-coded entry handling with the generic xfer
> function.
>
> This series was tested on an Ampere Mt. Jade reference system. The
> series cleanly applies to kvm/queue (note that this is deliberate as the
> generic kvm stats patches have not yet propagated to kvm-arm/queue) at
> the following commit:
>
> 8ad5e63649ff ("KVM: Don't take mmu_lock for range invalidation unless necessary")
>
> v1 -> v2:
>  - Address Jing's comment
>  - Carry Jing's r-b tag
>
> v2 -> v3:
>  - Roll all exit conditions into kvm_vcpu_exit_request() (Marc)
>  - Avoid needlessly checking for work twice (Marc)
>
> v1: http://lore.kernel.org/r/20210729195632.489978-1-oupton@google.com
> v2: http://lore.kernel.org/r/20210729220916.1672875-1-oupton@google.com
>
> Oliver Upton (3):
>   KVM: arm64: Record number of signal exits as a vCPU stat
>   entry: KVM: Allow use of generic KVM entry w/o full generic support
>   KVM: arm64: Use generic KVM xfer to guest work function
>
>  arch/arm64/include/asm/kvm_host.h |  1 +
>  arch/arm64/kvm/Kconfig            |  1 +
>  arch/arm64/kvm/arm.c              | 71 +++++++++++++++++++------------
>  arch/arm64/kvm/guest.c            |  1 +
>  include/linux/entry-kvm.h         |  6 ++-
>  5 files changed, 52 insertions(+), 28 deletions(-)
>
> --
> 2.32.0.554.ge1b32706d8-goog
>
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Re: [PATCH v3 0/3] KVM: arm64: Use generic guest entry infrastructure

[Marc Zyngier]

On Sun, 15 Aug 2021 08:50:09 +0100,
Oliver Upton <oupton@google.com> wrote:
> 
> Friendly ping :)

Ah, thanks for reminding me of this. I'll have a look again early next
week.

	M.

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Re: [PATCH v3 0/3] KVM: arm64: Use generic guest entry infrastructure

[Marc Zyngier]

On Mon, 2 Aug 2021 19:28:06 +0000, Oliver Upton wrote:
> The arm64 kernel doesn't yet support the full generic entry
> infrastructure. That being said, KVM/arm64 doesn't properly handle
> TIF_NOTIFY_RESUME and could pick this up by switching to the generic
> guest entry infrasturture.
> 
> Patch 1 adds a missing vCPU stat to ARM64 to record the number of signal
> exits to userspace.
> 
> [...]

Applied to next, thanks!

[1/3] KVM: arm64: Record number of signal exits as a vCPU stat
      commit: fe5161d2c39b8c2801f0e786631460c6e8a1cae4
[2/3] entry: KVM: Allow use of generic KVM entry w/o full generic support
      commit: e1c6b9e1669e44fb7f9688e34e460b759e3b9187
[3/3] KVM: arm64: Use generic KVM xfer to guest work function
      commit: 6caa5812e2d126a0aa8a17816c1ba6f0a0c2b309

Cheers,

	M.
-- 
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