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From:   Srikar Dronamraju <srikar@linux.vnet.ibm.com>
To:     Michael Ellerman <mpe@ellerman.id.au>
Cc:     linuxppc-dev <linuxppc-dev@lists.ozlabs.org>,
        Srikar Dronamraju <srikar@linux.vnet.ibm.com>,
        LKML <linux-kernel@vger.kernel.org>,
        Nicholas Piggin <npiggin@gmail.com>,
        Nathan Lynch <nathanl@linux.ibm.com>,
        Gautham R Shenoy <ego@linux.vnet.ibm.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Valentin Schneider <valentin.schneider@arm.com>,
        Juri Lelli <juri.lelli@redhat.com>,
        Waiman Long <longman@redhat.com>, Phil Auld <pauld@redhat.com>
Subject: [PATCH v2 4/4] powerpc/paravirt: Use is_kvm_guest in vcpu_is_preempted
Date:   Wed,  2 Dec 2020 10:34:56 +0530
Message-Id: <20201202050456.164005-5-srikar@linux.vnet.ibm.com>
In-Reply-To: <20201202050456.164005-1-srikar@linux.vnet.ibm.com>
References: <20201202050456.164005-1-srikar@linux.vnet.ibm.com>
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If its a shared lpar but not a KVM guest, then see if the vCPU is
related to the calling vCPU. On PowerVM, only cores can be preempted.
So if one vCPU is a non-preempted state, we can decipher that all other
vCPUs sharing the same core are in non-preempted state.

Cc: linuxppc-dev <linuxppc-dev@lists.ozlabs.org>
Cc: LKML <linux-kernel@vger.kernel.org>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Nicholas Piggin <npiggin@gmail.com>
Cc: Nathan Lynch <nathanl@linux.ibm.com>
Cc: Gautham R Shenoy <ego@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Valentin Schneider <valentin.schneider@arm.com>
Cc: Juri Lelli <juri.lelli@redhat.com>
Cc: Waiman Long <longman@redhat.com>
Cc: Phil Auld <pauld@redhat.com>
Acked-by: Waiman Long <longman@redhat.com>
Signed-off-by: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
---
 arch/powerpc/include/asm/paravirt.h | 18 ++++++++++++++++++
 1 file changed, 18 insertions(+)

diff --git a/arch/powerpc/include/asm/paravirt.h b/arch/powerpc/include/asm/paravirt.h
index 9362c94fe3aa..edc08f04aef7 100644
--- a/arch/powerpc/include/asm/paravirt.h
+++ b/arch/powerpc/include/asm/paravirt.h
@@ -10,6 +10,9 @@
 #endif
 
 #ifdef CONFIG_PPC_SPLPAR
+#include <asm/kvm_guest.h>
+#include <asm/cputhreads.h>
+
 DECLARE_STATIC_KEY_FALSE(shared_processor);
 
 static inline bool is_shared_processor(void)
@@ -74,6 +77,21 @@ static inline bool vcpu_is_preempted(int cpu)
 {
 	if (!is_shared_processor())
 		return false;
+
+#ifdef CONFIG_PPC_SPLPAR
+	if (!is_kvm_guest()) {
+		int first_cpu = cpu_first_thread_sibling(smp_processor_id());
+
+		/*
+		 * Preemption can only happen at core granularity. This CPU
+		 * is not preempted if one of the CPU of this core is not
+		 * preempted.
+		 */
+		if (cpu_first_thread_sibling(cpu) == first_cpu)
+			return false;
+	}
+#endif
+
 	if (yield_count_of(cpu) & 1)
 		return true;
 	return false;
-- 
2.18.4