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KVM: Xen PV-on-HVM guest support

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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>
This commit is contained in:
Ed Swierk 2009-10-15 15:21:43 -07:00 • committed by Avi Kivity
parent 94c30d9ca6
commit ffde22ac53
5 changed files with 89 additions and 0 deletions
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16
include/linux/kvm.h
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@ -436,6 +436,9 @@ struct kvm_ioeventfd {
#endif
#define KVM_CAP_IOEVENTFD 36
#define KVM_CAP_SET_IDENTITY_MAP_ADDR 37
#ifdef __KVM_HAVE_XEN_HVM
#define KVM_CAP_XEN_HVM 38
#endif
#ifdef KVM_CAP_IRQ_ROUTING
@ -488,6 +491,18 @@ struct kvm_x86_mce {
};
#endif
#ifdef KVM_CAP_XEN_HVM
struct kvm_xen_hvm_config {
__u32 flags;
__u32 msr;
__u64 blob_addr_32;
__u64 blob_addr_64;
__u8 blob_size_32;
__u8 blob_size_64;
__u8 pad2[30];
};
#endif
#define KVM_IRQFD_FLAG_DEASSIGN (1 << 0)
struct kvm_irqfd {
@ -546,6 +561,7 @@ struct kvm_irqfd {
#define KVM_CREATE_PIT2 _IOW(KVMIO, 0x77, struct kvm_pit_config)
#define KVM_SET_BOOT_CPU_ID _IO(KVMIO, 0x78)
#define KVM_IOEVENTFD _IOW(KVMIO, 0x79, struct kvm_ioeventfd)
#define KVM_XEN_HVM_CONFIG _IOW(KVMIO, 0x7a, struct kvm_xen_hvm_config)
/*
* ioctls for vcpu fds