From: Vaibhav Jain <vaibhav@linux.ibm.com>
To: linuxppc-dev@lists.ozlabs.org, kvm@vger.kernel.org,
kvm-ppc@vger.kernel.org
Cc: Vaibhav Jain <vaibhav@linux.ibm.com>,
Nicholas Piggin <npiggin@gmail.com>,
Michael Ellerman <mpe@ellerman.id.au>,
Jordan Niethe <jniethe5@gmail.com>,
Vaidyanathan Srinivasan <svaidy@linux.vnet.ibm.com>,
mikey@neuling.org, paulus@ozlabs.org, sbhat@linux.ibm.com,
gautam@linux.ibm.com, kconsul@linux.vnet.ibm.com,
amachhiw@linux.vnet.ibm.com, David.Laight@ACULAB.COM
Subject: [PATCH] KVM: PPC: Book3S HV nestedv2: Cancel pending HDEC exception
Date: Wed, 13 Mar 2024 12:56:23 +0530 [thread overview]
Message-ID: <20240313072625.76804-1-vaibhav@linux.ibm.com> (raw)
This reverts commit 180c6b072bf360b686e53d893d8dcf7dbbaec6bb ("KVM: PPC:
Book3S HV nestedv2: Do not cancel pending decrementer exception") which
prevented cancelling a pending HDEC exception for nestedv2 KVM guests. It
was done to avoid overhead of a H_GUEST_GET_STATE hcall to read the 'HDEC
expiry TB' register which was higher compared to handling extra decrementer
exceptions.
This overhead of reading 'HDEC expiry TB' register has been mitigated
recently by the L0 hypervisor(PowerVM) by putting the value of this
register in L2 guest-state output buffer on trap to L1. From there the
value of this register is cached, made available in kvmhv_run_single_vcpu()
to compare it against host(L1) timebase and cancel the pending hypervisor
decrementer exception if needed.
Fixes: 180c6b072bf3 ("KVM: PPC: Book3S HV nestedv2: Do not cancel pending decrementer exception")
Signed-off-by: Vaibhav Jain <vaibhav@linux.ibm.com>
---
arch/powerpc/kvm/book3s_hv.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/arch/powerpc/kvm/book3s_hv.c b/arch/powerpc/kvm/book3s_hv.c
index 0b921704da45..e47b954ce266 100644
--- a/arch/powerpc/kvm/book3s_hv.c
+++ b/arch/powerpc/kvm/book3s_hv.c
@@ -4856,7 +4856,7 @@ int kvmhv_run_single_vcpu(struct kvm_vcpu *vcpu, u64 time_limit,
* entering a nested guest in which case the decrementer is now owned
* by L2 and the L1 decrementer is provided in hdec_expires
*/
- if (!kvmhv_is_nestedv2() && kvmppc_core_pending_dec(vcpu) &&
+ if (kvmppc_core_pending_dec(vcpu) &&
((tb < kvmppc_dec_expires_host_tb(vcpu)) ||
(trap == BOOK3S_INTERRUPT_SYSCALL &&
kvmppc_get_gpr(vcpu, 3) == H_ENTER_NESTED)))
--
2.44.0
next reply other threads:[~2024-03-13 7:27 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-03-13 7:26 Vaibhav Jain [this message]
2024-03-20 13:43 ` [PATCH] KVM: PPC: Book3S HV nestedv2: Cancel pending HDEC exception Nicholas Piggin
2024-04-04 8:35 ` Linux regression tracking (Thorsten Leemhuis)
2024-04-05 3:20 ` Michael Ellerman
2024-04-05 5:54 ` Thorsten Leemhuis
2024-04-08 5:20 ` Michael Ellerman
2024-04-10 4:28 ` Nicholas Piggin
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