Hypercall code page is specified in the Hyper-V TLFS to be an overlay
page, ie., guest chooses a GPA and the host _places_ a page at that
location, making it visible to the guest and the existing page becomes
inaccessible. Similarly when disabled, the host should _remove_ the
overlay and the old page should become visible to the guest.
Until now, KVM patched the hypercall code directly into the guest
chosen GPA which is incorrect; instead, use the new user space MSR
filtering feature to trap hypercall page MSR writes, overlay it as
requested and then invoke a KVM_SET_MSR from user space to bounce back
control KVM. This bounce back is needed as KVM may have to write data
into the newly overlaid page.
Signed-off-by: Siddharth Chandrasekaran <sidcha@xxxxxxxxx>
---
hw/hyperv/hyperv.c | 10 ++++-
include/hw/hyperv/hyperv.h | 5 +++
target/i386/kvm/hyperv.c | 84 ++++++++++++++++++++++++++++++++++++++
target/i386/kvm/hyperv.h | 4 ++
target/i386/kvm/kvm.c | 26 +++++++++++-
5 files changed, 127 insertions(+), 2 deletions(-)
diff --git a/hw/hyperv/hyperv.c b/hw/hyperv/hyperv.c
index ac45e8e139..aa5ac5226e 100644
--- a/hw/hyperv/hyperv.c
+++ b/hw/hyperv/hyperv.c
@@ -36,6 +36,7 @@ struct SynICState {
OBJECT_DECLARE_SIMPLE_TYPE(SynICState, SYNIC)
static bool synic_enabled;
+struct hyperv_overlay_page hcall_page;
static void alloc_overlay_page(struct hyperv_overlay_page *overlay,
Object *owner, const char *name)
@@ -50,7 +51,7 @@ static void alloc_overlay_page(struct hyperv_overlay_page *overlay,
* This method must be called with iothread lock taken as it modifies
* the memory hierarchy.
*/
-static void hyperv_overlay_update(struct hyperv_overlay_page *overlay, hwaddr addr)
+void hyperv_overlay_update(struct hyperv_overlay_page *overlay, hwaddr addr)
{
if (addr != HYPERV_INVALID_OVERLAY_GPA) {
/* check if overlay page is enabled */
@@ -70,6 +71,13 @@ static void hyperv_overlay_update(struct hyperv_overlay_page *overlay, hwaddr ad
}
}
+void hyperv_overlay_init(void)
+{
+ memory_region_init_ram(&hcall_page.mr, NULL, "hyperv.hcall_page",
+ qemu_real_host_page_size, &error_abort);
+ hcall_page.addr = HYPERV_INVALID_OVERLAY_GPA;
+}
+
static void synic_update(SynICState *synic, bool enable,
hwaddr msg_page_addr, hwaddr event_page_addr)
{
diff --git a/include/hw/hyperv/hyperv.h b/include/hw/hyperv/hyperv.h
index d989193e84..f444431a81 100644
--- a/include/hw/hyperv/hyperv.h
+++ b/include/hw/hyperv/hyperv.h
@@ -85,6 +85,11 @@ static inline uint32_t hyperv_vp_index(CPUState *cs)
return cs->cpu_index;
}
+extern struct hyperv_overlay_page hcall_page;
+
+void hyperv_overlay_init(void);
+void hyperv_overlay_update(struct hyperv_overlay_page *page, hwaddr addr);
+
void hyperv_synic_add(CPUState *cs);
void hyperv_synic_reset(CPUState *cs);
void hyperv_synic_update(CPUState *cs, bool enable,
diff --git a/target/i386/kvm/hyperv.c b/target/i386/kvm/hyperv.c
index f49ed2621d..01c9c2468c 100644
--- a/target/i386/kvm/hyperv.c
+++ b/target/i386/kvm/hyperv.c
@@ -16,6 +16,76 @@
#include "hyperv.h"
#include "hw/hyperv/hyperv.h"
#include "hyperv-proto.h"
+#include "kvm_i386.h"
+
+struct x86_hv_overlay {
+ struct hyperv_overlay_page *page;
+ uint32_t msr;
+ hwaddr gpa;
+};
+
+static void async_overlay_update(CPUState *cs, run_on_cpu_data data)
+{
+ X86CPU *cpu = X86_CPU(cs);
+ struct x86_hv_overlay *overlay = data.host_ptr;
+
+ qemu_mutex_lock_iothread();
+ hyperv_overlay_update(overlay->page, overlay->gpa);
+ qemu_mutex_unlock_iothread();
+
+ /**
+ * Call KVM so it can keep a copy of the MSR data and do other post-overlay
+ * actions such as filling the overlay page contents before returning to
+ * guest. This works because MSR filtering is inactive for KVM_SET_MSRS
+ */
+ kvm_put_one_msr(cpu, overlay->msr, overlay->gpa);
+
+ g_free(overlay);
+}
+
+static void do_overlay_update(X86CPU *cpu, struct hyperv_overlay_page *page,
+ uint32_t msr, uint64_t data)
+{
+ struct x86_hv_overlay *overlay = g_malloc(sizeof(struct x86_hv_overlay));
+
+ *overlay = (struct x86_hv_overlay) {
+ .page = page,
+ .msr = msr,
+ .gpa = data
+ };
+
+ /**
+ * This will run in this cpu thread before it returns to KVM, but in a
+ * safe environment (i.e. when all cpus are quiescent) -- this is
+ * necessary because memory hierarchy is being changed
+ */
+ async_safe_run_on_cpu(CPU(cpu), async_overlay_update,
+ RUN_ON_CPU_HOST_PTR(overlay));
+}
+
+static void overlay_update(X86CPU *cpu, uint32_t msr, uint64_t data)
+{
+ switch (msr) {
+ case HV_X64_MSR_GUEST_OS_ID:
+ /**
+ * When GUEST_OS_ID is cleared, hypercall overlay should be removed;
+ * otherwise it is a NOP. We still need to do a SET_MSR here as the
+ * kernel need to keep a copy of data.
+ */
+ if (data != 0) {
+ kvm_put_one_msr(cpu, msr, data);
+ return;
+ }
+ /* Fake a zero write to the overlay page hcall to invalidate the mapping */
+ do_overlay_update(cpu, &hcall_page, msr, 0);
+ break;
+ case HV_X64_MSR_HYPERCALL:
+ do_overlay_update(cpu, &hcall_page, msr, data);
+ break;
+ default:
+ return;
+ }
+}
int hyperv_x86_synic_add(X86CPU *cpu)
{
@@ -44,6 +114,20 @@ static void async_synic_update(CPUState *cs, run_on_cpu_data data)
qemu_mutex_unlock_iothread();
}
+int kvm_hv_handle_wrmsr(X86CPU *cpu, uint32_t msr, uint64_t data)
+{
+ switch (msr) {
+ case HV_X64_MSR_GUEST_OS_ID:
+ case HV_X64_MSR_HYPERCALL:
+ overlay_update(cpu, msr, data);
+ break;
+ default:
+ return -1;
+ }
+
+ return 0;
+}
+
int kvm_hv_handle_exit(X86CPU *cpu, struct kvm_hyperv_exit *exit)
{
CPUX86State *env = &cpu->env;
diff --git a/target/i386/kvm/hyperv.h b/target/i386/kvm/hyperv.h
index 67543296c3..8e90fa949f 100644
--- a/target/i386/kvm/hyperv.h
+++ b/target/i386/kvm/hyperv.h
@@ -20,8 +20,12 @@
#ifdef CONFIG_KVM
int kvm_hv_handle_exit(X86CPU *cpu, struct kvm_hyperv_exit *exit);
+int kvm_hv_handle_wrmsr(X86CPU *cpu, uint32_t msr, uint64_t data);
+
#endif
+void hyperv_x86_hcall_page_update(X86CPU *cpu);
+
int hyperv_x86_synic_add(X86CPU *cpu);
void hyperv_x86_synic_reset(X86CPU *cpu);
void hyperv_x86_synic_update(X86CPU *cpu);
diff --git a/target/i386/kvm/kvm.c b/target/i386/kvm/kvm.c
index 3591f8cecc..bfb9eff440 100644
--- a/target/i386/kvm/kvm.c
+++ b/target/i386/kvm/kvm.c
@@ -2333,6 +2333,10 @@ int kvm_arch_init(MachineState *ms, KVMState *s)
}
}
+ if (has_hyperv && msr_filters_active) {
+ hyperv_overlay_init();
+ }
+
return 0;
}
@@ -4608,7 +4612,27 @@ static bool host_supports_vmx(void)
static int kvm_handle_wrmsr(X86CPU *cpu, struct kvm_run *run)
{
- return 0;
+ int r = -1;
+ uint32_t msr;
+ uint64_t data;
+
+ if (run->msr.reason != KVM_MSR_EXIT_REASON_FILTER) {
+ return -1;
+ }
+
+ msr = run->msr.index;
+ data = run->msr.data;
+
+ switch (msr) {
+ case HV_X64_MSR_GUEST_OS_ID:
+ case HV_X64_MSR_HYPERCALL:
+ r = kvm_hv_handle_wrmsr(cpu, msr, data);
+ break;
+ default:
+ error_report("Unknown MSR exit");
+ }
+
+ return r;
