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Message-Id: <20231121180223.12484-11-paul@xen.org>
Date: Tue, 21 Nov 2023 18:02:18 +0000
From: Paul Durrant <paul@....org>
To: David Woodhouse <dwmw2@...radead.org>, Paul Durrant <paul@....org>,
Sean Christopherson <seanjc@...gle.com>,
Paolo Bonzini <pbonzini@...hat.com>,
Thomas Gleixner <tglx@...utronix.de>,
Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
"H. Peter Anvin" <hpa@...or.com>, kvm@...r.kernel.org,
linux-kernel@...r.kernel.org
Subject: [PATCH v8 10/15] KVM: xen: allow vcpu_info to be mapped by fixed HVA
From: Paul Durrant <pdurrant@...zon.com>
If the guest does not explicitly set the GPA of vcpu_info structure in
memory then, for guests with 32 vCPUs or fewer, the vcpu_info embedded
in the shared_info page may be used. As described in a previous commit,
the shared_info page is an overlay at a fixed HVA within the VMM, so in
this case it also more optimal to activate the vcpu_info cache with a
fixed HVA to avoid unnecessary invalidation if the guest memory layout
is modified.
Signed-off-by: Paul Durrant <pdurrant@...zon.com>
Reviewed-by: David Woodhouse <dwmw@...zon.co.uk>
---
Cc: David Woodhouse <dwmw2@...radead.org>
Cc: Sean Christopherson <seanjc@...gle.com>
Cc: Paolo Bonzini <pbonzini@...hat.com>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: Ingo Molnar <mingo@...hat.com>
Cc: Borislav Petkov <bp@...en8.de>
Cc: Dave Hansen <dave.hansen@...ux.intel.com>
Cc: "H. Peter Anvin" <hpa@...or.com>
Cc: x86@...nel.org
v8:
- Re-base.
v5:
- New in this version.
---
Documentation/virt/kvm/api.rst | 26 +++++++++++++++++++++-----
arch/x86/kvm/xen.c | 34 ++++++++++++++++++++++++++++------
include/uapi/linux/kvm.h | 3 +++
3 files changed, 52 insertions(+), 11 deletions(-)
diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst
index 25ac75b6d8c5..2c9d6bbba051 100644
--- a/Documentation/virt/kvm/api.rst
+++ b/Documentation/virt/kvm/api.rst
@@ -5516,11 +5516,12 @@ KVM_XEN_ATTR_TYPE_SHARED_INFO
Sets the guest physical frame number at which the Xen shared_info
page resides. Note that although Xen places vcpu_info for the first
32 vCPUs in the shared_info page, KVM does not automatically do so
- and instead requires that KVM_XEN_VCPU_ATTR_TYPE_VCPU_INFO be used
- explicitly even when the vcpu_info for a given vCPU resides at the
- "default" location in the shared_info page. This is because KVM may
- not be aware of the Xen CPU id which is used as the index into the
- vcpu_info[] array, so may know the correct default location.
+ and instead requires that KVM_XEN_VCPU_ATTR_TYPE_VCPU_INFO or
+ KVM_XEN_VCPU_ATTR_TYPE_VCPU_INFO_HVA be used explicitly even when
+ the vcpu_info for a given vCPU resides at the "default" location
+ in the shared_info page. This is because KVM may not be aware of
+ the Xen CPU id which is used as the index into the vcpu_info[]
+ array, so may know the correct default location.
Note that the shared_info page may be constantly written to by KVM;
it contains the event channel bitmap used to deliver interrupts to
@@ -5642,6 +5643,21 @@ KVM_XEN_VCPU_ATTR_TYPE_VCPU_INFO
on dirty logging. Setting the gpa to KVM_XEN_INVALID_GPA will disable
the vcpu_info.
+KVM_XEN_VCPU_ATTR_TYPE_VCPU_INFO_HVA
+ If the KVM_XEN_HVM_CONFIG_SHARED_INFO_HVA flag is also set in the
+ Xen capabilities, then this attribute may be used to set the
+ userspace address of the vcpu_info for a given vCPU. It should
+ only be used when the vcpu_info resides at the "default" location
+ in the shared_info page. In this case it is safe to assume the
+ userspace address will not change, because the shared_info page is
+ an overlay on guest memory and remains at a fixed host address
+ regardless of where it is mapped in guest physical address space
+ and hence unnecessary invalidation of an internal cache may be
+ avoided if the guest memory layout is modified.
+ If the vcpu_info does not reside at the "default" location then
+ it is not guaranteed to remain at the same host address and
+ hence the aforementioned cache invalidation is required.
+
KVM_XEN_VCPU_ATTR_TYPE_VCPU_TIME_INFO
Sets the guest physical address of an additional pvclock structure
for a given vCPU. This is typically used for guest vsyscall support.
diff --git a/arch/x86/kvm/xen.c b/arch/x86/kvm/xen.c
index 618ae4c0e7f8..42a9f1ea25b3 100644
--- a/arch/x86/kvm/xen.c
+++ b/arch/x86/kvm/xen.c
@@ -759,20 +759,33 @@ int kvm_xen_vcpu_set_attr(struct kvm_vcpu *vcpu, struct kvm_xen_vcpu_attr *data)
switch (data->type) {
case KVM_XEN_VCPU_ATTR_TYPE_VCPU_INFO:
+ case KVM_XEN_VCPU_ATTR_TYPE_VCPU_INFO_HVA:
/* No compat necessary here. */
BUILD_BUG_ON(sizeof(struct vcpu_info) !=
sizeof(struct compat_vcpu_info));
BUILD_BUG_ON(offsetof(struct vcpu_info, time) !=
offsetof(struct compat_vcpu_info, time));
- if (data->u.gpa == KVM_XEN_INVALID_GPA) {
- kvm_gpc_deactivate(&vcpu->arch.xen.vcpu_info_cache);
- r = 0;
- break;
+ if (data->type == KVM_XEN_VCPU_ATTR_TYPE_VCPU_INFO) {
+ if (data->u.gpa == KVM_XEN_INVALID_GPA) {
+ kvm_gpc_deactivate(&vcpu->arch.xen.vcpu_info_cache);
+ r = 0;
+ break;
+ }
+
+ r = kvm_gpc_activate(&vcpu->arch.xen.vcpu_info_cache,
+ data->u.gpa, sizeof(struct vcpu_info));
+ } else {
+ if (data->u.hva == 0) {
+ kvm_gpc_deactivate(&vcpu->arch.xen.vcpu_info_cache);
+ r = 0;
+ break;
+ }
+
+ r = kvm_gpc_activate_hva(&vcpu->arch.xen.vcpu_info_cache,
+ data->u.hva, sizeof(struct vcpu_info));
}
- r = kvm_gpc_activate(&vcpu->arch.xen.vcpu_info_cache,
- data->u.gpa, sizeof(struct vcpu_info));
if (!r)
kvm_make_request(KVM_REQ_CLOCK_UPDATE, vcpu);
@@ -1001,6 +1014,15 @@ int kvm_xen_vcpu_get_attr(struct kvm_vcpu *vcpu, struct kvm_xen_vcpu_attr *data)
r = 0;
break;
+ case KVM_XEN_VCPU_ATTR_TYPE_VCPU_INFO_HVA:
+ if (vcpu->arch.xen.vcpu_info_cache.active &&
+ vcpu->arch.xen.vcpu_info_cache.gpa == KVM_XEN_INVALID_GPA)
+ data->u.hva = vcpu->arch.xen.vcpu_info_cache.uhva;
+ else
+ data->u.hva = 0;
+ r = 0;
+ break;
+
case KVM_XEN_VCPU_ATTR_TYPE_VCPU_TIME_INFO:
if (vcpu->arch.xen.vcpu_time_info_cache.active)
data->u.gpa = vcpu->arch.xen.vcpu_time_info_cache.gpa;
diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
index 769361b91f95..bb9d40b5e613 100644
--- a/include/uapi/linux/kvm.h
+++ b/include/uapi/linux/kvm.h
@@ -1869,6 +1869,7 @@ struct kvm_xen_vcpu_attr {
union {
__u64 gpa;
#define KVM_XEN_INVALID_GPA ((__u64)-1)
+ __u64 hva;
__u64 pad[8];
struct {
__u64 state;
@@ -1899,6 +1900,8 @@ struct kvm_xen_vcpu_attr {
#define KVM_XEN_VCPU_ATTR_TYPE_VCPU_ID 0x6
#define KVM_XEN_VCPU_ATTR_TYPE_TIMER 0x7
#define KVM_XEN_VCPU_ATTR_TYPE_UPCALL_VECTOR 0x8
+/* Available with KVM_CAP_XEN_HVM / KVM_XEN_HVM_CONFIG_SHARED_INFO_HVA */
+#define KVM_XEN_VCPU_ATTR_TYPE_VCPU_INFO_HVA 0x9
/* Secure Encrypted Virtualization command */
enum sev_cmd_id {
--
2.39.2
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