x86/kvm: Handle async page faults directly through do_page_fault()

KVM overloads #PF to indicate two types of not-actually-page-fault
events.  Right now, the KVM guest code intercepts them by modifying
the IDT and hooking the #PF vector.  This makes the already fragile
fault code even harder to understand, and it also pollutes call
traces with async_page_fault and do_async_page_fault for normal page
faults.

Clean it up by moving the logic into do_page_fault() using a static
branch.  This gets rid of the platform trap_init override mechanism
completely.

[ tglx: Fixed up 32bit, removed error code from the async functions and
  	massaged coding style ]

Signed-off-by: Andy Lutomirski <luto@kernel.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Alexandre Chartre <alexandre.chartre@oracle.com>
Acked-by: Paolo Bonzini <pbonzini@redhat.com>
Acked-by: Peter Zijlstra <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20200505134059.169270470@linutronix.de

1 files changed, 17 insertions, 2 deletions

diff --git a/arch/x86/include/asm/kvm_para.h b/arch/x86/include/asm/kvm_para.h
index 9b4df6eaa11a..5261363adda3 100644
--- a/arch/x86/include/asm/kvm_para.h
+++ b/arch/x86/include/asm/kvm_para.h
@@ -91,8 +91,18 @@ unsigned int kvm_arch_para_hints(void);
 void kvm_async_pf_task_wait(u32 token, int interrupt_kernel);
 void kvm_async_pf_task_wake(u32 token);
 u32 kvm_read_and_reset_pf_reason(void);
-extern void kvm_disable_steal_time(void);
-void do_async_page_fault(struct pt_regs *regs, unsigned long error_code, unsigned long address);
+void kvm_disable_steal_time(void);
+bool __kvm_handle_async_pf(struct pt_regs *regs, u32 token);
+
+DECLARE_STATIC_KEY_FALSE(kvm_async_pf_enabled);
+
+static __always_inline bool kvm_handle_async_pf(struct pt_regs *regs, u32 token)
+{
+	if (static_branch_unlikely(&kvm_async_pf_enabled))
+		return __kvm_handle_async_pf(regs, token);
+	else
+		return false;
+}
 
 #ifdef CONFIG_PARAVIRT_SPINLOCKS
 void __init kvm_spinlock_init(void);
@@ -130,6 +140,11 @@ static inline void kvm_disable_steal_time(void)
 {
 	return;
 }
+
+static inline bool kvm_handle_async_pf(struct pt_regs *regs, u32 token)
+{
+	return false;
+}
 #endif
 
 #endif /* _ASM_X86_KVM_PARA_H */