i386/xen: implement HYPERVISOR_memory_op

Specifically XENMEM_add_to_physmap with space XENMAPSPACE_shared_info to
allow the guest to set its shared_info page.

Signed-off-by: Joao Martins <joao.m.martins@oracle.com>
[dwmw2: Use the xen_overlay device, add compat support]
Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
Reviewed-by: Paul Durrant <paul@xen.org>

target/i386/kvm/trace-events

@@ -9,3 +9,4 @@ kvm_x86_update_msi_routes(int num) "Updated %d MSI routes"
 # xen-emu.c
 kvm_xen_hypercall(int cpu, uint8_t cpl, uint64_t input, uint64_t a0, uint64_t a1, uint64_t a2, uint64_t ret) "xen_hypercall: cpu %d cpl %d input %" PRIu64 " a0 0x%" PRIx64 " a1 0x%" PRIx64 " a2 0x%" PRIx64" ret 0x%" PRIx64
 kvm_xen_soft_reset(void) ""
+kvm_xen_set_shared_info(uint64_t gfn) "shared info at gfn 0x%" PRIx64

target/i386/kvm/xen-compat.h

@@ -0,0 +1,27 @@
+/*
+ * Xen HVM emulation support in KVM
+ *
+ * Copyright © 2022 Amazon.com, Inc. or its affiliates. All Rights Reserved.
+ *
+ * This work is licensed under the terms of the GNU GPL, version 2 or later.
+ * See the COPYING file in the top-level directory.
+ *
+ */
+
+#ifndef QEMU_I386_KVM_XEN_COMPAT_H
+#define QEMU_I386_KVM_XEN_COMPAT_H
+
+#include "hw/xen/interface/memory.h"
+
+typedef uint32_t compat_pfn_t;
+typedef uint32_t compat_ulong_t;
+
+struct compat_xen_add_to_physmap {
+    domid_t domid;
+    uint16_t size;
+    unsigned int space;
+    compat_ulong_t idx;
+    compat_pfn_t gpfn;
+};
+
+#endif /* QEMU_I386_XEN_COMPAT_H */

target/i386/kvm/xen-emu.c

@@ -12,6 +12,7 @@
 #include "qemu/osdep.h"
 #include "qemu/log.h"
 #include "qemu/main-loop.h"
+#include "hw/xen/xen.h"
 #include "sysemu/kvm_int.h"
 #include "sysemu/kvm_xen.h"
 #include "kvm/kvm_i386.h"
@@ -24,6 +25,15 @@
 
 #include "hw/xen/interface/version.h"
 #include "hw/xen/interface/sched.h"
+#include "hw/xen/interface/memory.h"
+
+#include "xen-compat.h"
+
+#ifdef TARGET_X86_64
+#define hypercall_compat32(longmode) (!(longmode))
+#else
+#define hypercall_compat32(longmode) (false)
+#endif
 
 static int kvm_gva_rw(CPUState *cs, uint64_t gva, void *_buf, size_t sz,
                       bool is_write)
@@ -175,13 +185,114 @@ static bool kvm_xen_hcall_xen_version(struct kvm_xen_exit *exit, X86CPU *cpu,
     return true;
 }
 
+static int xen_set_shared_info(uint64_t gfn)
+{
+    uint64_t gpa = gfn << TARGET_PAGE_BITS;
+    int err;
+
+    QEMU_IOTHREAD_LOCK_GUARD();
+
+    /*
+     * The xen_overlay device tells KVM about it too, since it had to
+     * do that on migration load anyway (unless we're going to jump
+     * through lots of hoops to maintain the fiction that this isn't
+     * KVM-specific.
+     */
+    err = xen_overlay_map_shinfo_page(gpa);
+    if (err) {
+            return err;
+    }
+
+    trace_kvm_xen_set_shared_info(gfn);
+
+    return err;
+}
+
+static int add_to_physmap_one(uint32_t space, uint64_t idx, uint64_t gfn)
+{
+    switch (space) {
+    case XENMAPSPACE_shared_info:
+        if (idx > 0) {
+            return -EINVAL;
+        }
+        return xen_set_shared_info(gfn);
+
+    case XENMAPSPACE_grant_table:
+    case XENMAPSPACE_gmfn:
+    case XENMAPSPACE_gmfn_range:
+        return -ENOTSUP;
+
+    case XENMAPSPACE_gmfn_foreign:
+    case XENMAPSPACE_dev_mmio:
+        return -EPERM;
+
+    default:
+        return -EINVAL;
+    }
+}
+
+static int do_add_to_physmap(struct kvm_xen_exit *exit, X86CPU *cpu,
+                             uint64_t arg)
+{
+    struct xen_add_to_physmap xatp;
+    CPUState *cs = CPU(cpu);
+
+    if (hypercall_compat32(exit->u.hcall.longmode)) {
+        struct compat_xen_add_to_physmap xatp32;
+
+        qemu_build_assert(sizeof(struct compat_xen_add_to_physmap) == 16);
+        if (kvm_copy_from_gva(cs, arg, &xatp32, sizeof(xatp32))) {
+            return -EFAULT;
+        }
+        xatp.domid = xatp32.domid;
+        xatp.size = xatp32.size;
+        xatp.space = xatp32.space;
+        xatp.idx = xatp32.idx;
+        xatp.gpfn = xatp32.gpfn;
+    } else {
+        if (kvm_copy_from_gva(cs, arg, &xatp, sizeof(xatp))) {
+            return -EFAULT;
+        }
+    }
+
+    if (xatp.domid != DOMID_SELF && xatp.domid != xen_domid) {
+        return -ESRCH;
+    }
+
+    return add_to_physmap_one(xatp.space, xatp.idx, xatp.gpfn);
+}
+
+static bool kvm_xen_hcall_memory_op(struct kvm_xen_exit *exit, X86CPU *cpu,
+                                   int cmd, uint64_t arg)
+{
+    int err;
+
+    switch (cmd) {
+    case XENMEM_add_to_physmap:
+        err = do_add_to_physmap(exit, cpu, arg);
+        break;
+
+    default:
+        return false;
+    }
+
+    exit->u.hcall.result = err;
+    return true;
+}
+
 int kvm_xen_soft_reset(void)
 {
+    int err;
+
     assert(qemu_mutex_iothread_locked());
 
     trace_kvm_xen_soft_reset();
 
-    /* Nothing to reset... yet. */
+    err = xen_overlay_map_shinfo_page(INVALID_GFN);
+    if (err) {
+        return err;
+    }
+
     return 0;
 }
 
@@ -270,6 +381,9 @@ static bool do_kvm_xen_handle_exit(X86CPU *cpu, struct kvm_xen_exit *exit)
     case __HYPERVISOR_sched_op:
         return kvm_xen_hcall_sched_op(exit, cpu, exit->u.hcall.params[0],
                                       exit->u.hcall.params[1]);
+    case __HYPERVISOR_memory_op:
+        return kvm_xen_hcall_memory_op(exit, cpu, exit->u.hcall.params[0],
+                                       exit->u.hcall.params[1]);
     case __HYPERVISOR_xen_version:
         return kvm_xen_hcall_xen_version(exit, cpu, exit->u.hcall.params[0],
                                          exit->u.hcall.params[1]);