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[RFC PATCH v4 16/47] i386/xen: manage and save/restore Xen guest long_mo
From: |
David Woodhouse |
Subject: |
[RFC PATCH v4 16/47] i386/xen: manage and save/restore Xen guest long_mode setting |
Date: |
Wed, 21 Dec 2022 01:05:52 +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>
---
hw/i386/kvm/xen_overlay.c | 65 +++++++++++++++++++++++++++++++++++++++
hw/i386/kvm/xen_overlay.h | 4 +++
target/i386/kvm/xen-emu.c | 12 ++++++++
3 files changed, 81 insertions(+)
diff --git a/hw/i386/kvm/xen_overlay.c b/hw/i386/kvm/xen_overlay.c
index 331dea6b8b..7046bd55f1 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_map_page_locked(&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()
}
};
@@ -198,3 +216,50 @@ 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)
+{
+ if (xen_overlay_singleton) {
+ return xen_overlay_singleton->long_mode;
+ }
+ return false;
+}
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 80005ea527..80f09f33df 100644
--- a/target/i386/kvm/xen-emu.c
+++ b/target/i386/kvm/xen-emu.c
@@ -19,6 +19,8 @@
#include "trace.h"
#include "sysemu/runstate.h"
+#include "hw/i386/kvm/xen_overlay.h"
+
#include "standard-headers/xen/version.h"
#include "standard-headers/xen/sched.h"
@@ -274,6 +276,16 @@ 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
--
2.35.3
- [RFC PATCH v4 06/47] i386/hvm: Set Xen vCPU ID in KVM, (continued)
- [RFC PATCH v4 06/47] i386/hvm: Set Xen vCPU ID in KVM, David Woodhouse, 2022/12/20
- [RFC PATCH v4 36/47] hw/xen: Implement EVTCHNOP_bind_interdomain, David Woodhouse, 2022/12/20
- [RFC PATCH v4 07/47] xen-platform: exclude vfio-pci from the PCI platform unplug, David Woodhouse, 2022/12/20
- [RFC PATCH v4 10/47] i386/xen: handle guest hypercalls, David Woodhouse, 2022/12/20
- [RFC PATCH v4 42/47] kvm/i386: Add xen-gnttab-max-frames property, David Woodhouse, 2022/12/20
- [RFC PATCH v4 28/47] i386/xen: Add support for Xen event channel delivery to vCPU, David Woodhouse, 2022/12/20
- [RFC PATCH v4 18/47] i386/xen: implement XENMEM_add_to_physmap_batch, David Woodhouse, 2022/12/20
- [RFC PATCH v4 09/47] hw/xen_backend: refactor xen_be_init(), David Woodhouse, 2022/12/20
- [RFC PATCH v4 04/47] i386/kvm: Add xen-version KVM accelerator property and init KVM Xen support, David Woodhouse, 2022/12/20
- [RFC PATCH v4 23/47] i386/xen: handle VCPUOP_register_runstate_memory_area, David Woodhouse, 2022/12/20
- [RFC PATCH v4 16/47] i386/xen: manage and save/restore Xen guest long_mode setting,
David Woodhouse <=
- [RFC PATCH v4 26/47] i386/xen: implement HVMOP_set_param, David Woodhouse, 2022/12/20
- [RFC PATCH v4 17/47] i386/xen: implement HYPERVISOR_memory_op, David Woodhouse, 2022/12/20
- [RFC PATCH v4 08/47] xen-platform: allow its creation with XEN_EMULATE mode, David Woodhouse, 2022/12/20
- [RFC PATCH v4 32/47] hw/xen: Implement EVTCHNOP_bind_virq, David Woodhouse, 2022/12/20
- [RFC PATCH v4 29/47] hw/xen: Implement EVTCHNOP_status, David Woodhouse, 2022/12/20
- [RFC PATCH v4 45/47] i386/xen: Implement HYPERVISOR_grant_table_op and GNTTABOP_[gs]et_verson, David Woodhouse, 2022/12/20
- [RFC PATCH v4 38/47] hw/xen: Implement EVTCHNOP_reset, David Woodhouse, 2022/12/20