[PATCH v10 10/19] KVM: xen: (re-)initialize shared_info if guest (32/64-bit) mode is set

Paul Durrant
2023-12-04T15:00:31Z

If the shared_info PFN cache has already been initialized then the content
of the shared_info page needs to be (re-)initialized whenever the guest
mode is (re)set.
Setting the guest mode is either done explicitly by the VMM via the
KVM_XEN_ATTR_TYPE_LONG_MODE attribute, or implicitly when the guest writes
the MSR to set up the hypercall page.

Signed-off-by: Paul Durrant <pdurrant@amazon.com>
---
Cc: Sean Christopherson <seanjc@google.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: David Woodhouse <dwmw2@infradead.org>
Cc: x86@kernel.org

v10:
- New in this version.
---
arch/x86/kvm/xen.c | 36 +++++++++++++++++++++++++++++-------
1 file changed, 29 insertions(+), 7 deletions(-)

diff --git a/arch/x86/kvm/xen.c b/arch/x86/kvm/xen.c
index 9351b32cfcba..3aa452a71890 100644
--- a/arch/x86/kvm/xen.c
+++ b/arch/x86/kvm/xen.c
@@ -623,10 +623,20 @@ int kvm_xen_hvm_set_attr(struct kvm *kvm, struct kvm_xen_hvm_attr *data)
if (!IS_ENABLED(CONFIG_64BIT) && data->u.long_mode) {
r = -EINVAL;
} else {
+ bool lm = !!data->u.long_mode;
+
mutex_lock(&kvm->arch.xen.xen_lock);
- kvm->arch.xen.long_mode = !!data->u.long_mode;
+ if (kvm->arch.xen.long_mode != lm) {
+ kvm->arch.xen.long_mode = lm;
+
+ /*
+ * Re-initialize shared_info to put the wallclock in the
+ * correct place.
+ */
+ r = kvm->arch.xen.shinfo_cache.active ?
+ kvm_xen_shared_info_init(kvm) : 0;
+ }
mutex_unlock(&kvm->arch.xen.xen_lock);
- r = 0;
}
break;

@@ -648,9 +658,6 @@ int kvm_xen_hvm_set_attr(struct kvm *kvm, struct kvm_xen_hvm_attr *data)

srcu_read_unlock(&kvm->srcu, idx);

- if (!r && kvm->arch.xen.shinfo_cache.active)
- r = kvm_xen_shared_info_init(kvm);
-
mutex_unlock(&kvm->arch.xen.xen_lock);
break;
}
@@ -1101,9 +1108,24 @@ int kvm_xen_write_hypercall_page(struct kvm_vcpu *vcpu, u64 data)
u32 page_num = data & ~PAGE_MASK;
u64 page_addr = data & PAGE_MASK;
bool lm = is_long_mode(vcpu);
+ int r = 0;
+
+ mutex_lock(&kvm->arch.xen.xen_lock);
+ if (kvm->arch.xen.long_mode != lm) {
+ kvm->arch.xen.long_mode = lm;
+
+ /*
+ * Re-initialize shared_info to put the wallclock in the
+ * correct place.
+ */
+ if (kvm->arch.xen.shinfo_cache.active &&
+ kvm_xen_shared_info_init(kvm))
+ r = 1;
+ }
+ mutex_unlock(&kvm->arch.xen.xen_lock);

- /* Latch long_mode for shared_info pages etc. */
- vcpu->kvm->arch.xen.long_mode = lm;
+ if (r)
+ return r;

/*
* If Xen hypercall intercept is enabled, fill the hypercall
--
2.39.2