From: Paul Durrant <paul@xen.org>
To: Paolo Bonzini <pbonzini@redhat.com>,
Jonathan Corbet <corbet@lwn.net>,
Sean Christopherson <seanjc@google.com>,
Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
Dave Hansen <dave.hansen@linux.intel.com>,
x86@kernel.org, "H. Peter Anvin" <hpa@zytor.com>,
David Woodhouse <dwmw2@infradead.org>,
Paul Durrant <paul@xen.org>, Shuah Khan <shuah@kernel.org>,
kvm@vger.kernel.org, linux-doc@vger.kernel.org,
linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org
Subject: [PATCH v10 18/19] KVM: pfncache: check the need for invalidation under read lock first
Date: Mon, 4 Dec 2023 14:43:33 +0000 [thread overview]
Message-ID: <20231204144334.910-19-paul@xen.org> (raw)
In-Reply-To: <20231204144334.910-1-paul@xen.org>
From: Paul Durrant <pdurrant@amazon.com>
Taking a write lock on a pfncache will be disruptive if the cache is
heavily used (which only requires a read lock). Hence, in the MMU notifier
callback, take read locks on caches to check for a match; only taking a
write lock to actually perform an invalidation (after a another check).
Signed-off-by: Paul Durrant <pdurrant@amazon.com>
---
Cc: Sean Christopherson <seanjc@google.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: David Woodhouse <dwmw2@infradead.org>
v10:
- New in this version.
---
virt/kvm/pfncache.c | 22 +++++++++++++++++++---
1 file changed, 19 insertions(+), 3 deletions(-)
diff --git a/virt/kvm/pfncache.c b/virt/kvm/pfncache.c
index c2a2d1e145b6..4da16d494f4b 100644
--- a/virt/kvm/pfncache.c
+++ b/virt/kvm/pfncache.c
@@ -29,14 +29,30 @@ void gfn_to_pfn_cache_invalidate_start(struct kvm *kvm, unsigned long start,
spin_lock(&kvm->gpc_lock);
list_for_each_entry(gpc, &kvm->gpc_list, list) {
- write_lock_irq(&gpc->lock);
+ read_lock_irq(&gpc->lock);
/* Only a single page so no need to care about length */
if (gpc->valid && !is_error_noslot_pfn(gpc->pfn) &&
gpc->uhva >= start && gpc->uhva < end) {
- gpc->valid = false;
+ read_unlock_irq(&gpc->lock);
+
+ /*
+ * There is a small window here where the cache could
+ * be modified, and invalidation would no longer be
+ * necessary. Hence check again whether invalidation
+ * is still necessary once the write lock has been
+ * acquired.
+ */
+
+ write_lock_irq(&gpc->lock);
+ if (gpc->valid && !is_error_noslot_pfn(gpc->pfn) &&
+ gpc->uhva >= start && gpc->uhva < end)
+ gpc->valid = false;
+ write_unlock_irq(&gpc->lock);
+ continue;
}
- write_unlock_irq(&gpc->lock);
+
+ read_unlock_irq(&gpc->lock);
}
spin_unlock(&kvm->gpc_lock);
}
--
2.39.2
next prev parent reply other threads:[~2023-12-04 15:00 UTC|newest]
Thread overview: 27+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-12-04 14:43 [PATCH v10 00/19] KVM: xen: update shared_info and vcpu_info handling Paul Durrant
2023-12-04 14:43 ` [PATCH v10 01/19] KVM: pfncache: Add a map helper function Paul Durrant
2023-12-04 14:43 ` [PATCH v10 02/19] KVM: pfncache: remove unnecessary exports Paul Durrant
2023-12-04 14:43 ` [PATCH v10 03/19] KVM: xen: mark guest pages dirty with the pfncache lock held Paul Durrant
2023-12-04 14:43 ` [PATCH v10 04/19] KVM: pfncache: add a mark-dirty helper Paul Durrant
2023-12-04 14:43 ` [PATCH v10 05/19] KVM: pfncache: remove KVM_GUEST_USES_PFN usage Paul Durrant
2023-12-04 14:43 ` [PATCH v10 06/19] KVM: pfncache: stop open-coding offset_in_page() Paul Durrant
2023-12-04 14:43 ` [PATCH v10 07/19] KVM: pfncache: include page offset in uhva and use it consistently Paul Durrant
2023-12-04 14:43 ` [PATCH v10 08/19] KVM: pfncache: allow a cache to be activated with a fixed (userspace) HVA Paul Durrant
2023-12-04 14:43 ` [PATCH v10 09/19] KVM: xen: separate initialization of shared_info cache and content Paul Durrant
2023-12-14 13:41 ` David Woodhouse
2023-12-14 14:00 ` Paul Durrant
2023-12-04 14:43 ` [PATCH v10 10/19] KVM: xen: (re-)initialize shared_info if guest (32/64-bit) mode is set Paul Durrant
2023-12-14 13:44 ` David Woodhouse
2023-12-04 14:43 ` [PATCH v10 11/19] KVM: xen: allow shared_info to be mapped by fixed HVA Paul Durrant
2023-12-04 14:43 ` [PATCH v10 12/19] KVM: xen: allow vcpu_info " Paul Durrant
2023-12-04 14:43 ` [PATCH v10 13/19] KVM: selftests / xen: map shared_info using HVA rather than GFN Paul Durrant
2023-12-04 14:43 ` [PATCH v10 14/19] KVM: selftests / xen: re-map vcpu_info using HVA rather than GPA Paul Durrant
2023-12-04 14:43 ` [PATCH v10 15/19] KVM: xen: advertize the KVM_XEN_HVM_CONFIG_SHARED_INFO_HVA capability Paul Durrant
2023-12-04 14:43 ` [PATCH v10 16/19] KVM: xen: split up kvm_xen_set_evtchn_fast() Paul Durrant
2023-12-14 14:00 ` David Woodhouse
2023-12-14 14:20 ` David Woodhouse
2023-12-04 14:43 ` [PATCH v10 17/19] KVM: xen: don't block on pfncache locks in kvm_xen_set_evtchn_fast() Paul Durrant
2023-12-14 14:03 ` David Woodhouse
2023-12-04 14:43 ` Paul Durrant [this message]
2023-12-14 14:08 ` [PATCH v10 18/19] KVM: pfncache: check the need for invalidation under read lock first David Woodhouse
2023-12-04 14:43 ` [PATCH v10 19/19] KVM: xen: allow vcpu_info content to be 'safely' copied Paul Durrant
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