linux-kernel - [PATCH 1/2] powerpc: kvm: use generic transfer to guest mode work

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Message-ID: <20250421102837.78515-2-sshegde@linux.ibm.com>
Date: Mon, 21 Apr 2025 15:58:36 +0530
From: Shrikanth Hegde <sshegde@...ux.ibm.com>
To: maddy@...ux.ibm.com, linuxppc-dev@...ts.ozlabs.org
Cc: npiggin@...il.com, christophe.leroy@...roup.eu, sshegde@...ux.ibm.com,
        gautam@...ux.ibm.com, vaibhav@...ux.ibm.com, bigeasy@...utronix.de,
        linux-kernel@...r.kernel.org
Subject: [PATCH 1/2] powerpc: kvm: use generic transfer to guest mode work

There is generic entry framework to handle signals and check for
reschedule etc before entering the guest. Use that framework for
powerpc.

Advantages:
- Less code duplication.
- powerpc kvm now understands NR and NR_lazy bits.
- powerpc can enable HAVE_POSIX_CPU_TIMERS_TASK_WORK, currently the
  powerpc/kvm code doesn't handle TIF_NOTIFY_RESUME.

Testing: No splats seen in below cases.
- Booted KVM guest on PowerVM and PowerNV systems. 
- Ran stress-ng CPU stressors in each above case. 
- On PowerNV host, tried preempt=lazy/full and run stress-ng CPU stressor
  in the KVM guest. 

Signed-off-by: Shrikanth Hegde <sshegde@...ux.ibm.com>
---
 arch/powerpc/Kconfig         |  1 +
 arch/powerpc/kvm/book3s_hv.c | 13 +++++++------
 arch/powerpc/kvm/powerpc.c   | 22 ++++++++--------------
 3 files changed, 16 insertions(+), 20 deletions(-)

diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
index 6722625a4..83807ae44 100644
--- a/arch/powerpc/Kconfig
+++ b/arch/powerpc/Kconfig
@@ -299,6 +299,7 @@ config PPC
 	select IRQ_DOMAIN
 	select IRQ_FORCED_THREADING
 	select KASAN_VMALLOC			if KASAN && EXECMEM
+	select KVM_XFER_TO_GUEST_WORK
 	select LOCK_MM_AND_FIND_VMA
 	select MMU_GATHER_PAGE_SIZE
 	select MMU_GATHER_RCU_TABLE_FREE
diff --git a/arch/powerpc/kvm/book3s_hv.c b/arch/powerpc/kvm/book3s_hv.c
index 19f4d298d..123539642 100644
--- a/arch/powerpc/kvm/book3s_hv.c
+++ b/arch/powerpc/kvm/book3s_hv.c
@@ -80,8 +80,8 @@
 #include <asm/ultravisor.h>
 #include <asm/dtl.h>
 #include <asm/plpar_wrappers.h>
-
 #include <trace/events/ipi.h>
+#include <linux/entry-kvm.h>
 
 #include "book3s.h"
 #include "book3s_hv.h"
@@ -4901,7 +4901,7 @@ int kvmhv_run_single_vcpu(struct kvm_vcpu *vcpu, u64 time_limit,
 	}
 
 	if (need_resched())
-		cond_resched();
+		schedule();
 
 	kvmppc_update_vpas(vcpu);
 
@@ -5097,10 +5097,11 @@ static int kvmppc_vcpu_run_hv(struct kvm_vcpu *vcpu)
 		return -EINVAL;
 	}
 
-	/* No need to go into the guest when all we'll do is come back out */
-	if (signal_pending(current)) {
-		run->exit_reason = KVM_EXIT_INTR;
-		return -EINTR;
+	/* use generic frameworks to handle signals, need_resched  */
+	if (__xfer_to_guest_mode_work_pending()) {
+		r = xfer_to_guest_mode_handle_work(vcpu);
+		if (r)
+			return r;
 	}
 
 #ifdef CONFIG_PPC_TRANSACTIONAL_MEM
diff --git a/arch/powerpc/kvm/powerpc.c b/arch/powerpc/kvm/powerpc.c
index 153587741..4ff334532 100644
--- a/arch/powerpc/kvm/powerpc.c
+++ b/arch/powerpc/kvm/powerpc.c
@@ -34,6 +34,7 @@
 #endif
 #include <asm/ultravisor.h>
 #include <asm/setup.h>
+#include <linux/entry-kvm.h>
 
 #include "timing.h"
 #include "../mm/mmu_decl.h"
@@ -80,24 +81,17 @@ int kvmppc_prepare_to_enter(struct kvm_vcpu *vcpu)
 {
 	int r;
 
+	/* use generic framework to handle need resched and signals */
+	if (__xfer_to_guest_mode_work_pending()) {
+		r = xfer_to_guest_mode_handle_work(vcpu);
+		if (r)
+			return r;
+	}
+
 	WARN_ON(irqs_disabled());
 	hard_irq_disable();
 
 	while (true) {
-		if (need_resched()) {
-			local_irq_enable();
-			cond_resched();
-			hard_irq_disable();
-			continue;
-		}
-
-		if (signal_pending(current)) {
-			kvmppc_account_exit(vcpu, SIGNAL_EXITS);
-			vcpu->run->exit_reason = KVM_EXIT_INTR;
-			r = -EINTR;
-			break;
-		}
-
 		vcpu->mode = IN_GUEST_MODE;
 
 		/*
-- 
2.48.1