KVM: x86: Support the vCPU preemption check with nopvspin and realtime hint

If guest kernel is configured with nopvspin, or CONFIG_PARAVIRT_SPINLOCK
is disabled, or guest find its has dedicated pCPUs from realtime hint
feature, the pvspinlock will be disabled, and vCPU preemption check
is disabled too.

Hoever, KVM still can emulating HLT for vCPU for both cases.  Checking if a vCPU
is preempted or not can still boost performance in IPI-heavy scenarios such as
unixbench file copy and pipe-based context switching tests:  Here the vCPU is
running with a dedicated pCPU, so the guest kernel has nopvspin but is
emulating HLT for the vCPU:

Testcase                                  Base    with patch
System Benchmarks Index Values            INDEX     INDEX
Dhrystone 2 using register variables     3278.4    3277.7
Double-Precision Whetstone                822.8     825.8
Execl Throughput                         1296.5     941.1
File Copy 1024 bufsize 2000 maxblocks    2124.2    2142.7
File Copy 256 bufsize 500 maxblocks      1335.9    1353.6
File Copy 4096 bufsize 8000 maxblocks    4256.3    4760.3
Pipe Throughput                          1050.1    1054.0
Pipe-based Context Switching              243.3     352.0
Process Creation                          820.1     814.4
Shell Scripts (1 concurrent)             2169.0    2086.0
Shell Scripts (8 concurrent)             7710.3    7576.3
System Call Overhead                      672.4     673.9
                                      ========    =======
System Benchmarks Index Score             1467.2   1483.0

Move the setting of pv_ops.lock.vcpu_is_preempted to kvm_guest_init, so
that it does not depend on pvspinlock.

Signed-off-by: Li RongQing <lirongqing@baidu.com>
Message-Id: <1646815610-43315-1-git-send-email-lirongqing@baidu.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

2 files changed, 40 insertions, 39 deletions

diff --git a/arch/x86/kernel/asm-offsets_64.c b/arch/x86/kernel/asm-offsets_64.c
index b14533af7676..9b698215d261 100644
--- a/arch/x86/kernel/asm-offsets_64.c
+++ b/arch/x86/kernel/asm-offsets_64.c
@@ -5,7 +5,7 @@
 
 #include <asm/ia32.h>
 
-#if defined(CONFIG_KVM_GUEST) && defined(CONFIG_PARAVIRT_SPINLOCKS)
+#if defined(CONFIG_KVM_GUEST)
 #include <asm/kvm_para.h>
 #endif
 
@@ -20,7 +20,7 @@ int main(void)
 	BLANK();
 #endif
 
-#if defined(CONFIG_KVM_GUEST) && defined(CONFIG_PARAVIRT_SPINLOCKS)
+#if defined(CONFIG_KVM_GUEST)
 	OFFSET(KVM_STEAL_TIME_preempted, kvm_steal_time, preempted);
 	BLANK();
 #endif
diff --git a/arch/x86/kernel/kvm.c b/arch/x86/kernel/kvm.c
index ed8a13ac4ab2..774d924aeda8 100644
--- a/arch/x86/kernel/kvm.c
+++ b/arch/x86/kernel/kvm.c
@@ -752,6 +752,41 @@ static void kvm_crash_shutdown(struct pt_regs *regs)
 }
 #endif
 
+#if defined(CONFIG_X86_32) || !defined(CONFIG_SMP)
+bool __kvm_vcpu_is_preempted(long cpu);
+
+__visible bool __kvm_vcpu_is_preempted(long cpu)
+{
+	struct kvm_steal_time *src = &per_cpu(steal_time, cpu);
+
+	return !!(src->preempted & KVM_VCPU_PREEMPTED);
+}
+PV_CALLEE_SAVE_REGS_THUNK(__kvm_vcpu_is_preempted);
+
+#else
+
+#include <asm/asm-offsets.h>
+
+extern bool __raw_callee_save___kvm_vcpu_is_preempted(long);
+
+/*
+ * Hand-optimize version for x86-64 to avoid 8 64-bit register saving and
+ * restoring to/from the stack.
+ */
+asm(
+".pushsection .text;"
+".global __raw_callee_save___kvm_vcpu_is_preempted;"
+".type __raw_callee_save___kvm_vcpu_is_preempted, @function;"
+"__raw_callee_save___kvm_vcpu_is_preempted:"
+"movq	__per_cpu_offset(,%rdi,8), %rax;"
+"cmpb	$0, " __stringify(KVM_STEAL_TIME_preempted) "+steal_time(%rax);"
+"setne	%al;"
+"ret;"
+".size __raw_callee_save___kvm_vcpu_is_preempted, .-__raw_callee_save___kvm_vcpu_is_preempted;"
+".popsection");
+
+#endif
+
 static void __init kvm_guest_init(void)
 {
 	int i;
@@ -764,6 +799,9 @@ static void __init kvm_guest_init(void)
 	if (kvm_para_has_feature(KVM_FEATURE_STEAL_TIME)) {
 		has_steal_clock = 1;
 		static_call_update(pv_steal_clock, kvm_steal_clock);
+
+		pv_ops.lock.vcpu_is_preempted =
+			PV_CALLEE_SAVE(__kvm_vcpu_is_preempted);
 	}
 
 	if (kvm_para_has_feature(KVM_FEATURE_PV_EOI))
@@ -1005,39 +1043,6 @@ static void kvm_wait(u8 *ptr, u8 val)
 	}
 }
 
-#ifdef CONFIG_X86_32
-__visible bool __kvm_vcpu_is_preempted(long cpu)
-{
-	struct kvm_steal_time *src = &per_cpu(steal_time, cpu);
-
-	return !!(src->preempted & KVM_VCPU_PREEMPTED);
-}
-PV_CALLEE_SAVE_REGS_THUNK(__kvm_vcpu_is_preempted);
-
-#else
-
-#include <asm/asm-offsets.h>
-
-extern bool __raw_callee_save___kvm_vcpu_is_preempted(long);
-
-/*
- * Hand-optimize version for x86-64 to avoid 8 64-bit register saving and
- * restoring to/from the stack.
- */
-asm(
-".pushsection .text;"
-".global __raw_callee_save___kvm_vcpu_is_preempted;"
-".type __raw_callee_save___kvm_vcpu_is_preempted, @function;"
-"__raw_callee_save___kvm_vcpu_is_preempted:"
-"movq	__per_cpu_offset(,%rdi,8), %rax;"
-"cmpb	$0, " __stringify(KVM_STEAL_TIME_preempted) "+steal_time(%rax);"
-"setne	%al;"
-"ret;"
-".size __raw_callee_save___kvm_vcpu_is_preempted, .-__raw_callee_save___kvm_vcpu_is_preempted;"
-".popsection");
-
-#endif
-
 /*
  * Setup pv_lock_ops to exploit KVM_FEATURE_PV_UNHALT if present.
  */
@@ -1081,10 +1086,6 @@ void __init kvm_spinlock_init(void)
 	pv_ops.lock.wait = kvm_wait;
 	pv_ops.lock.kick = kvm_kick_cpu;
 
-	if (kvm_para_has_feature(KVM_FEATURE_STEAL_TIME)) {
-		pv_ops.lock.vcpu_is_preempted =
-			PV_CALLEE_SAVE(__kvm_vcpu_is_preempted);
-	}
 	/*
 	 * When PV spinlock is enabled which is preferred over
 	 * virt_spin_lock(), virt_spin_lock_key's value is meaningless.