From: Sean Christopherson <seanjc@google.com>
To: Paolo Bonzini <pbonzini@redhat.com>
Cc: Sean Christopherson <seanjc@google.com>,
Vitaly Kuznetsov <vkuznets@redhat.com>,
Wanpeng Li <wanpengli@tencent.com>,
Jim Mattson <jmattson@google.com>, Joerg Roedel <joro@8bytes.org>,
kvm@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: [PATCH 2/2] KVM: x86: Take KVM's SRCU lock only if steal time update is needed
Date: Fri, 22 Jan 2021 16:03:34 -0800 [thread overview]
Message-ID: <20210123000334.3123628-3-seanjc@google.com> (raw)
In-Reply-To: <20210123000334.3123628-1-seanjc@google.com>
Enter a SRCU critical section for a memslots lookup during steal time
update if and only if a steal time update is actually needed. Taking
the lock can be avoided if steal time is disabled by the guest, or if
KVM knows it has already flagged the vCPU as being preempted.
Reword the comment to be more precise as to exactly why memslots will
be queried.
Signed-off-by: Sean Christopherson <seanjc@google.com>
---
arch/x86/kvm/x86.c | 20 +++++++++++---------
1 file changed, 11 insertions(+), 9 deletions(-)
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 3f4b09d9f25b..4efaa858a8bb 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -4005,6 +4005,7 @@ static void kvm_steal_time_set_preempted(struct kvm_vcpu *vcpu)
{
struct kvm_host_map map;
struct kvm_steal_time *st;
+ int idx;
if (!(vcpu->arch.st.msr_val & KVM_MSR_ENABLED))
return;
@@ -4012,9 +4013,15 @@ static void kvm_steal_time_set_preempted(struct kvm_vcpu *vcpu)
if (vcpu->arch.st.preempted)
return;
+ /*
+ * Take the srcu lock as memslots will be accessed to check the gfn
+ * cache generation against the memslots generation.
+ */
+ idx = srcu_read_lock(&vcpu->kvm->srcu);
+
if (kvm_map_gfn(vcpu, vcpu->arch.st.msr_val >> PAGE_SHIFT, &map,
&vcpu->arch.st.cache, true))
- return;
+ goto out;
st = map.hva +
offset_in_page(vcpu->arch.st.msr_val & KVM_STEAL_VALID_BITS);
@@ -4022,22 +4029,17 @@ static void kvm_steal_time_set_preempted(struct kvm_vcpu *vcpu)
st->preempted = vcpu->arch.st.preempted = KVM_VCPU_PREEMPTED;
kvm_unmap_gfn(vcpu, &map, &vcpu->arch.st.cache, true, true);
+
+out:
+ srcu_read_unlock(&vcpu->kvm->srcu, idx);
}
void kvm_arch_vcpu_put(struct kvm_vcpu *vcpu)
{
- int idx;
-
if (vcpu->preempted && !vcpu->arch.guest_state_protected)
vcpu->arch.preempted_in_kernel = !kvm_x86_ops.get_cpl(vcpu);
- /*
- * kvm_memslots() will be called by
- * kvm_write_guest_offset_cached() so take the srcu lock.
- */
- idx = srcu_read_lock(&vcpu->kvm->srcu);
kvm_steal_time_set_preempted(vcpu);
- srcu_read_unlock(&vcpu->kvm->srcu, idx);
kvm_x86_ops.vcpu_put(vcpu);
vcpu->arch.last_host_tsc = rdtsc();
/*
--
2.30.0.280.ga3ce27912f-goog
next prev parent reply other threads:[~2021-01-23 0:09 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-01-23 0:03 [PATCH 0/2] KVM: x86: Minor steal time cleanups Sean Christopherson
2021-01-23 0:03 ` [PATCH 1/2] KVM: x86: Remove obsolete disabling of page faults in kvm_arch_vcpu_put() Sean Christopherson
2021-01-23 0:03 ` Sean Christopherson [this message]
2021-01-25 17:23 ` [PATCH 0/2] KVM: x86: Minor steal time cleanups Paolo Bonzini
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20210123000334.3123628-3-seanjc@google.com \
--to=seanjc@google.com \
--cc=jmattson@google.com \
--cc=joro@8bytes.org \
--cc=kvm@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=pbonzini@redhat.com \
--cc=vkuznets@redhat.com \
--cc=wanpengli@tencent.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).