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KVM: x86/xen: allow vcpu_info to be mapped by fixed HVA

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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@amazon.com>
Reviewed-by: David Woodhouse <dwmw@amazon.co.uk>
Link: https://lore.kernel.org/r/20240215152916.1158-14-paul@xen.org
[sean: use kvm_gpc_is_{gpa,hva}_active()]
Signed-off-by: Sean Christopherson <seanjc@google.com>
This commit is contained in:
Paul Durrant 2024-02-15 15:29:08 +00:00 committed by Sean Christopherson
parent b9220d3279
commit 3991f35805
3 changed files with 52 additions and 12 deletions
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26
Documentation/virt/kvm/api.rst
View File

@ -5523,11 +5523,12 @@ 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
@ -5649,6 +5650,21 @@ 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.

3
arch/x86/include/uapi/asm/kvm.h
View File

@ -622,6 +622,7 @@ struct kvm_xen_vcpu_attr {
union {
__u64 gpa;
#define KVM_XEN_INVALID_GPA ((__u64)-1)
__u64 hva;
__u64 pad[8];
struct {
__u64 state;
@ -652,6 +653,8 @@ 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 {

35
arch/x86/kvm/xen.c
View File

@ -782,20 +782,33 @@ 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);
@ -1017,13 +1030,21 @@ int kvm_xen_vcpu_get_attr(struct kvm_vcpu *vcpu, struct kvm_xen_vcpu_attr *data)
switch (data->type) {
case KVM_XEN_VCPU_ATTR_TYPE_VCPU_INFO:
if (vcpu->arch.xen.vcpu_info_cache.active)
if (kvm_gpc_is_gpa_active(&vcpu->arch.xen.vcpu_info_cache))
data->u.gpa = vcpu->arch.xen.vcpu_info_cache.gpa;
else
data->u.gpa = KVM_XEN_INVALID_GPA;
r = 0;
break;
case KVM_XEN_VCPU_ATTR_TYPE_VCPU_INFO_HVA:
if (kvm_gpc_is_hva_active(&vcpu->arch.xen.vcpu_info_cache))
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;