linux-kernel - [PATCH v3 9/9] KVM: Move instrumentation-safe annotations for enter/exit to x86 code

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Date:   Thu, 15 Apr 2021 15:21:06 -0700
From:   Sean Christopherson <seanjc@...gle.com>
To:     Paolo Bonzini <pbonzini@...hat.com>
Cc:     Sean Christopherson <seanjc@...gle.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
        Michael Tokarev <mjt@....msk.ru>,
        Christian Borntraeger <borntraeger@...ibm.com>
Subject: [PATCH v3 9/9] KVM: Move instrumentation-safe annotations for
 enter/exit to x86 code

Drop the instrumentation_{begin,end}() annonations from the common KVM
guest enter/exit helpers, and massage the x86 code as needed to preserve
the necessary annotations.  x86 is the only architecture whose transition
flow is tagged as noinstr, and more specifically, it is the only
architecture for which instrumentation_{begin,end}() can be non-empty.

No other architecture supports CONFIG_STACK_VALIDATION=y, and s390 is the
only other architecture that support CONFIG_DEBUG_ENTRY=y.  For
instrumentation annontations to be meaningful, both aformentioned configs
must be enabled.

Letting x86 deal with the annotations avoids unnecessary nops by
squashing back-to-back instrumention-safe sequences.

Signed-off-by: Sean Christopherson <seanjc@...gle.com>
---
 arch/x86/kvm/x86.h       | 4 ++--
 include/linux/kvm_host.h | 9 +--------
 2 files changed, 3 insertions(+), 10 deletions(-)

diff --git a/arch/x86/kvm/x86.h b/arch/x86/kvm/x86.h
index 285953e81777..b17857ac540b 100644
--- a/arch/x86/kvm/x86.h
+++ b/arch/x86/kvm/x86.h
@@ -25,9 +25,9 @@ static __always_inline void kvm_guest_enter_irqoff(void)
 	instrumentation_begin();
 	trace_hardirqs_on_prepare();
 	lockdep_hardirqs_on_prepare(CALLER_ADDR0);
-	instrumentation_end();
-
 	guest_enter_irqoff();
+	instrumentation_end();
+
 	lockdep_hardirqs_on(CALLER_ADDR0);
 }
 
diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index 444d5f0225cb..e5eb64019f47 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -339,9 +339,7 @@ static __always_inline void guest_enter_irqoff(void)
 	 * This is running in ioctl context so its safe to assume that it's the
 	 * stime pending cputime to flush.
 	 */
-	instrumentation_begin();
 	vtime_account_guest_enter();
-	instrumentation_end();
 
 	/*
 	 * KVM does not hold any references to rcu protected data when it
@@ -351,21 +349,16 @@ static __always_inline void guest_enter_irqoff(void)
 	 * one time slice). Lets treat guest mode as quiescent state, just like
 	 * we do with user-mode execution.
 	 */
-	if (!context_tracking_guest_enter_irqoff()) {
-		instrumentation_begin();
+	if (!context_tracking_guest_enter_irqoff())
 		rcu_virt_note_context_switch(smp_processor_id());
-		instrumentation_end();
-	}
 }
 
 static __always_inline void guest_exit_irqoff(void)
 {
 	context_tracking_guest_exit_irqoff();
 
-	instrumentation_begin();
 	/* Flush the guest cputime we spent on the guest */
 	vtime_account_guest_exit();
-	instrumentation_end();
 }
 
 static inline void guest_exit(void)
-- 
2.31.1.368.gbe11c130af-goog