linux-kernel - [PATCH 4/4] powerpc/paravirt: Use is_kvm_guest in vcpu_is

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Date:   Wed, 28 Oct 2020 18:05:12 +0530
From:   Srikar Dronamraju <srikar@...ux.vnet.ibm.com>
To:     Michael Ellerman <mpe@...erman.id.au>
Cc:     linuxppc-dev <linuxppc-dev@...ts.ozlabs.org>,
        Srikar Dronamraju <srikar@...ux.vnet.ibm.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Nicholas Piggin <npiggin@...il.com>,
        Nathan Lynch <nathanl@...ux.ibm.com>,
        Gautham R Shenoy <ego@...ux.vnet.ibm.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Valentin Schneider <valentin.schneider@....com>,
        Juri Lelli <juri.lelli@...hat.com>,
        Waiman Long <longman@...hat.com>, Phil Auld <pauld@...hat.com>
Subject: [PATCH 4/4] powerpc/paravirt: Use is_kvm_guest in vcpu_is_preempted

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.

Signed-off-by: Srikar Dronamraju <srikar@...ux.vnet.ibm.com>
Cc: linuxppc-dev <linuxppc-dev@...ts.ozlabs.org>
Cc: LKML <linux-kernel@...r.kernel.org>
Cc: Michael Ellerman <mpe@...erman.id.au>
Cc: Nicholas Piggin <npiggin@...il.com>
Cc: Nathan Lynch <nathanl@...ux.ibm.com>
Cc: Gautham R Shenoy <ego@...ux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Valentin Schneider <valentin.schneider@....com>
Cc: Juri Lelli <juri.lelli@...hat.com>
Cc: Waiman Long <longman@...hat.com>
Cc: Phil Auld <pauld@...hat.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