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[PATCH v12 16/60] i386/xen: manage and save/restore Xen guest long_mode
From: |
David Woodhouse |
Subject: |
[PATCH v12 16/60] i386/xen: manage and save/restore Xen guest long_mode setting |
Date: |
Mon, 20 Feb 2023 20:46:52 +0000 |
From: David Woodhouse <dwmw@amazon.co.uk>
Xen will "latch" the guest's 32-bit or 64-bit ("long mode") setting when
the guest writes the MSR to fill in the hypercall page, or when the guest
sets the event channel callback in HVM_PARAM_CALLBACK_IRQ.
KVM handles the former and sets the kernel's long_mode flag accordingly.
The latter will be handled in userspace. Keep them in sync by noticing
when a hypercall is made in a mode that doesn't match qemu's idea of
the guest mode, and resyncing from the kernel. Do that same sync right
before serialization too, in case the guest has set the hypercall page
but hasn't yet made a system call.
Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
Reviewed-by: Paul Durrant <paul@xen.org>
---
hw/i386/kvm/xen_overlay.c | 62 +++++++++++++++++++++++++++++++++++++++
hw/i386/kvm/xen_overlay.h | 4 +++
target/i386/kvm/xen-emu.c | 12 ++++++++
3 files changed, 78 insertions(+)
diff --git a/hw/i386/kvm/xen_overlay.c b/hw/i386/kvm/xen_overlay.c
index a2441e2b4e..8685d87959 100644
--- a/hw/i386/kvm/xen_overlay.c
+++ b/hw/i386/kvm/xen_overlay.c
@@ -44,6 +44,7 @@ struct XenOverlayState {
MemoryRegion shinfo_mem;
void *shinfo_ptr;
uint64_t shinfo_gpa;
+ bool long_mode;
};
struct XenOverlayState *xen_overlay_singleton;
@@ -96,9 +97,21 @@ static void xen_overlay_realize(DeviceState *dev, Error
**errp)
s->shinfo_ptr = memory_region_get_ram_ptr(&s->shinfo_mem);
s->shinfo_gpa = INVALID_GPA;
+ s->long_mode = false;
memset(s->shinfo_ptr, 0, XEN_PAGE_SIZE);
}
+static int xen_overlay_pre_save(void *opaque)
+{
+ /*
+ * Fetch the kernel's idea of long_mode to avoid the race condition
+ * where the guest has set the hypercall page up in 64-bit mode but
+ * not yet made a hypercall by the time migration happens, so qemu
+ * hasn't yet noticed.
+ */
+ return xen_sync_long_mode();
+}
+
static int xen_overlay_post_load(void *opaque, int version_id)
{
XenOverlayState *s = opaque;
@@ -107,6 +120,9 @@ static int xen_overlay_post_load(void *opaque, int
version_id)
xen_overlay_do_map_page(&s->shinfo_mem, s->shinfo_gpa);
xen_overlay_set_be_shinfo(s->shinfo_gpa >> XEN_PAGE_SHIFT);
}
+ if (s->long_mode) {
+ xen_set_long_mode(true);
+ }
return 0;
}
@@ -121,9 +137,11 @@ static const VMStateDescription xen_overlay_vmstate = {
.version_id = 1,
.minimum_version_id = 1,
.needed = xen_overlay_is_needed,
+ .pre_save = xen_overlay_pre_save,
.post_load = xen_overlay_post_load,
.fields = (VMStateField[]) {
VMSTATE_UINT64(shinfo_gpa, XenOverlayState),
+ VMSTATE_BOOL(long_mode, XenOverlayState),
VMSTATE_END_OF_LIST()
}
};
@@ -208,3 +226,47 @@ void *xen_overlay_get_shinfo_ptr(void)
return s->shinfo_ptr;
}
+
+int xen_sync_long_mode(void)
+{
+ int ret;
+ struct kvm_xen_hvm_attr xa = {
+ .type = KVM_XEN_ATTR_TYPE_LONG_MODE,
+ };
+
+ if (!xen_overlay_singleton) {
+ return -ENOENT;
+ }
+
+ ret = kvm_vm_ioctl(kvm_state, KVM_XEN_HVM_GET_ATTR, &xa);
+ if (!ret) {
+ xen_overlay_singleton->long_mode = xa.u.long_mode;
+ }
+
+ return ret;
+}
+
+int xen_set_long_mode(bool long_mode)
+{
+ int ret;
+ struct kvm_xen_hvm_attr xa = {
+ .type = KVM_XEN_ATTR_TYPE_LONG_MODE,
+ .u.long_mode = long_mode,
+ };
+
+ if (!xen_overlay_singleton) {
+ return -ENOENT;
+ }
+
+ ret = kvm_vm_ioctl(kvm_state, KVM_XEN_HVM_SET_ATTR, &xa);
+ if (!ret) {
+ xen_overlay_singleton->long_mode = xa.u.long_mode;
+ }
+
+ return ret;
+}
+
+bool xen_is_long_mode(void)
+{
+ return xen_overlay_singleton && xen_overlay_singleton->long_mode;
+}
diff --git a/hw/i386/kvm/xen_overlay.h b/hw/i386/kvm/xen_overlay.h
index 00cff05bb0..5c46a0b036 100644
--- a/hw/i386/kvm/xen_overlay.h
+++ b/hw/i386/kvm/xen_overlay.h
@@ -17,4 +17,8 @@ void xen_overlay_create(void);
int xen_overlay_map_shinfo_page(uint64_t gpa);
void *xen_overlay_get_shinfo_ptr(void);
+int xen_sync_long_mode(void);
+int xen_set_long_mode(bool long_mode);
+bool xen_is_long_mode(void);
+
#endif /* QEMU_XEN_OVERLAY_H */
diff --git a/target/i386/kvm/xen-emu.c b/target/i386/kvm/xen-emu.c
index ebea27caf6..be6d85f2cb 100644
--- a/target/i386/kvm/xen-emu.c
+++ b/target/i386/kvm/xen-emu.c
@@ -20,6 +20,8 @@
#include "trace.h"
#include "sysemu/runstate.h"
+#include "hw/i386/kvm/xen_overlay.h"
+
#include "hw/xen/interface/version.h"
#include "hw/xen/interface/sched.h"
@@ -282,6 +284,16 @@ int kvm_xen_handle_exit(X86CPU *cpu, struct kvm_xen_exit
*exit)
return -1;
}
+ /*
+ * The kernel latches the guest 32/64 mode when the MSR is used to fill
+ * the hypercall page. So if we see a hypercall in a mode that doesn't
+ * match our own idea of the guest mode, fetch the kernel's idea of the
+ * "long mode" to remain in sync.
+ */
+ if (exit->u.hcall.longmode != xen_is_long_mode()) {
+ xen_sync_long_mode();
+ }
+
if (!do_kvm_xen_handle_exit(cpu, exit)) {
/*
* Some hypercalls will be deliberately "implemented" by returning
--
2.39.0
- [PATCH v12 51/60] hw/xen: Add xen_xenstore device for xenstore emulation, (continued)
- [PATCH v12 51/60] hw/xen: Add xen_xenstore device for xenstore emulation, David Woodhouse, 2023/02/20
- [PATCH v12 06/60] i386/hvm: Set Xen vCPU ID in KVM, David Woodhouse, 2023/02/20
- [PATCH v12 55/60] hw/xen: Implement emulated PIRQ hypercall support, David Woodhouse, 2023/02/20
- [PATCH v12 24/60] i386/xen: implement HYPERVISOR_event_channel_op, David Woodhouse, 2023/02/20
- [PATCH v12 56/60] hw/xen: Support GSI mapping to PIRQ, David Woodhouse, 2023/02/20
- [PATCH v12 09/60] i386/xen: handle guest hypercalls, David Woodhouse, 2023/02/20
- [PATCH v12 32/60] hw/xen: Implement EVTCHNOP_bind_virq, David Woodhouse, 2023/02/20
- [PATCH v12 21/60] i386/xen: handle VCPUOP_register_vcpu_info, David Woodhouse, 2023/02/20
- [PATCH v12 20/60] i386/xen: implement HYPERVISOR_vcpu_op, David Woodhouse, 2023/02/20
- [PATCH v12 01/60] include: import Xen public headers to hw/xen/interface, David Woodhouse, 2023/02/20
- [PATCH v12 16/60] i386/xen: manage and save/restore Xen guest long_mode setting,
David Woodhouse <=
- [PATCH v12 36/60] hw/xen: Implement EVTCHNOP_bind_interdomain, David Woodhouse, 2023/02/20
- [PATCH v12 47/60] i386/xen: handle PV timer hypercalls, David Woodhouse, 2023/02/20
- Re: [PATCH v12 47/60] i386/xen: handle PV timer hypercalls, David Woodhouse, 2023/02/22
- Re: [PATCH v12 47/60] i386/xen: handle PV timer hypercalls, Paul Durrant, 2023/02/22
- Re: [PATCH v12 47/60] i386/xen: handle PV timer hypercalls, Paul Durrant, 2023/02/22
- Re: [PATCH v12 47/60] i386/xen: handle PV timer hypercalls, David Woodhouse, 2023/02/22
- Re: [PATCH v12 47/60] i386/xen: handle PV timer hypercalls, Paul Durrant, 2023/02/22
- Re: [PATCH v12 47/60] i386/xen: handle PV timer hypercalls, Paul Durrant, 2023/02/22
- Re: [PATCH v12 47/60] i386/xen: handle PV timer hypercalls, David Woodhouse, 2023/02/22