KVM: Xen PV-on-HVM guest support
Support for Xen PV-on-HVM guests can be implemented almost entirely in
userspace, except for handling one annoying MSR that maps a Xen
hypercall blob into guest address space.
A generic mechanism to delegate MSR writes to userspace seems overkill
and risks encouraging similar MSR abuse in the future. Thus this patch
adds special support for the Xen HVM MSR.
I implemented a new ioctl, KVM_XEN_HVM_CONFIG, that lets userspace tell
KVM which MSR the guest will write to, as well as the starting address
and size of the hypercall blobs (one each for 32-bit and 64-bit) that
userspace has loaded from files. When the guest writes to the MSR, KVM
copies one page of the blob from userspace to the guest.
I've tested this patch with a hacked-up version of Gerd's userspace
code, booting a number of guests (CentOS 5.3 i386 and x86_64, and
FreeBSD 8.0-RC1 amd64) and exercising PV network and block devices.
[jan: fix i386 build warning]
[avi: future proof abi with a flags field]
Signed-off-by: Ed Swierk <eswierk@aristanetworks.com>
Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>
Signed-off-by: Avi Kivity <avi@redhat.com>
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 5d450cc..bb842db 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -857,6 +857,38 @@
return 0;
}
+static int xen_hvm_config(struct kvm_vcpu *vcpu, u64 data)
+{
+ struct kvm *kvm = vcpu->kvm;
+ int lm = is_long_mode(vcpu);
+ u8 *blob_addr = lm ? (u8 *)(long)kvm->arch.xen_hvm_config.blob_addr_64
+ : (u8 *)(long)kvm->arch.xen_hvm_config.blob_addr_32;
+ u8 blob_size = lm ? kvm->arch.xen_hvm_config.blob_size_64
+ : kvm->arch.xen_hvm_config.blob_size_32;
+ u32 page_num = data & ~PAGE_MASK;
+ u64 page_addr = data & PAGE_MASK;
+ u8 *page;
+ int r;
+
+ r = -E2BIG;
+ if (page_num >= blob_size)
+ goto out;
+ r = -ENOMEM;
+ page = kzalloc(PAGE_SIZE, GFP_KERNEL);
+ if (!page)
+ goto out;
+ r = -EFAULT;
+ if (copy_from_user(page, blob_addr + (page_num * PAGE_SIZE), PAGE_SIZE))
+ goto out_free;
+ if (kvm_write_guest(kvm, page_addr, page, PAGE_SIZE))
+ goto out_free;
+ r = 0;
+out_free:
+ kfree(page);
+out:
+ return r;
+}
+
int kvm_set_msr_common(struct kvm_vcpu *vcpu, u32 msr, u64 data)
{
switch (msr) {
@@ -972,6 +1004,8 @@
"0x%x data 0x%llx\n", msr, data);
break;
default:
+ if (msr && (msr == vcpu->kvm->arch.xen_hvm_config.msr))
+ return xen_hvm_config(vcpu, data);
if (!ignore_msrs) {
pr_unimpl(vcpu, "unhandled wrmsr: 0x%x data %llx\n",
msr, data);
@@ -1246,6 +1280,7 @@
case KVM_CAP_PIT2:
case KVM_CAP_PIT_STATE2:
case KVM_CAP_SET_IDENTITY_MAP_ADDR:
+ case KVM_CAP_XEN_HVM:
r = 1;
break;
case KVM_CAP_COALESCED_MMIO:
@@ -2441,6 +2476,17 @@
r = 0;
break;
}
+ case KVM_XEN_HVM_CONFIG: {
+ r = -EFAULT;
+ if (copy_from_user(&kvm->arch.xen_hvm_config, argp,
+ sizeof(struct kvm_xen_hvm_config)))
+ goto out;
+ r = -EINVAL;
+ if (kvm->arch.xen_hvm_config.flags)
+ goto out;
+ r = 0;
+ break;
+ }
default:
;
}