[Xen-devel] [PATCH v5 07/12] x86/hyperv: setup hypercall page

[Wei Liu <wl@xxxxxxx>]

Hyper-V uses a technique called overlay page for its hypercall page. It
will insert a backing page to the guest when the hypercall functionality
is enabled. That means we can use a page that is not backed by real
memory for hypercall page.

Use the top-most addressable page for that purpose. Adjust e820 code
accordingly.

We also need to register Xen's guest OS ID to Hyper-V. Use 0x3 as the
vendor ID. Fix the comment in hyperv-tlfs.h while at it.

Signed-off-by: Wei Liu <liuwe@xxxxxxxxxxxxx>
---
v5:
1. use hypervisor_reserve_top_pages
2. add a macro for hypercall page mfn
3. address other misc comments

v4:
1. Use fixmap
2. Follow routines listed in TLFS
---
 xen/arch/x86/e820.c                     |  5 +++
 xen/arch/x86/guest/hyperv/hyperv.c      | 57 +++++++++++++++++++++++--
 xen/include/asm-x86/guest/hyperv-tlfs.h |  5 ++-
 xen/include/asm-x86/guest/hyperv.h      |  3 ++
 4 files changed, 65 insertions(+), 5 deletions(-)

diff --git a/xen/arch/x86/e820.c b/xen/arch/x86/e820.c
index 3892c9cfb7..99643f3ea0 100644
--- a/xen/arch/x86/e820.c
+++ b/xen/arch/x86/e820.c
@@ -343,6 +343,7 @@ static unsigned long __init find_max_pfn(void)
 {
     unsigned int i;
     unsigned long max_pfn = 0;
+    unsigned long top_pfn = ((1ull << paddr_bits) - 1) >> PAGE_SHIFT;
 
     for (i = 0; i < e820.nr_map; i++) {
         unsigned long start, end;
@@ -357,6 +358,10 @@ static unsigned long __init find_max_pfn(void)
             max_pfn = end;
     }
 
+    top_pfn -= hypervisor_reserve_top_pages();
+    if ( max_pfn >= top_pfn )
+        max_pfn = top_pfn;
+
     return max_pfn;
 }
 
diff --git a/xen/arch/x86/guest/hyperv/hyperv.c 
b/xen/arch/x86/guest/hyperv/hyperv.c
index 8d38313d7a..2bedcc438c 100644
--- a/xen/arch/x86/guest/hyperv/hyperv.c
+++ b/xen/arch/x86/guest/hyperv/hyperv.c
@@ -19,15 +19,26 @@
  * Copyright (c) 2019 Microsoft.
  */
 #include <xen/init.h>
+#include <xen/version.h>
 
+#include <asm/fixmap.h>
 #include <asm/guest.h>
 #include <asm/guest/hyperv-tlfs.h>
+#include <asm/processor.h>
 
 struct ms_hyperv_info __read_mostly ms_hyperv;
 
-static const struct hypervisor_ops ops = {
-    .name = "Hyper-V",
-};
+static uint64_t generate_guest_id(void)
+{
+    uint64_t id;
+
+    id = (uint64_t)HV_XEN_VENDOR_ID << 48;
+    id |= (xen_major_version() << 16) | xen_minor_version();
+
+    return id;
+}
+
+static const struct hypervisor_ops ops;
 
 const struct hypervisor_ops *__init hyperv_probe(void)
 {
@@ -72,6 +83,46 @@ const struct hypervisor_ops *__init hyperv_probe(void)
     return &ops;
 }
 
+static void __init setup_hypercall_page(void)
+{
+    union hv_x64_msr_hypercall_contents hypercall_msr;
+    union hv_guest_os_id guest_id;
+    unsigned long mfn;
+
+    rdmsrl(HV_X64_MSR_GUEST_OS_ID, guest_id.raw);
+    if ( !guest_id.raw )
+    {
+        guest_id.raw = generate_guest_id();
+        wrmsrl(HV_X64_MSR_GUEST_OS_ID, guest_id.raw);
+    }
+
+    rdmsrl(HV_X64_MSR_HYPERCALL, hypercall_msr.as_uint64);
+    if ( !hypercall_msr.enable )
+    {
+        mfn = HV_HCALL_MFN;
+        hypercall_msr.enable = 1;
+        hypercall_msr.guest_physical_address = mfn;
+        wrmsrl(HV_X64_MSR_HYPERCALL, hypercall_msr.as_uint64);
+    } else {
+        mfn = hypercall_msr.guest_physical_address;
+    }
+
+    rdmsrl(HV_X64_MSR_HYPERCALL, hypercall_msr.as_uint64);
+    BUG_ON(!hypercall_msr.enable);
+
+    set_fixmap_x(FIX_X_HYPERV_HCALL, mfn << PAGE_SHIFT);
+}
+
+static void __init setup(void)
+{
+    setup_hypercall_page();
+}
+
+static const struct hypervisor_ops ops = {
+    .name = "Hyper-V",
+    .setup = setup,
+};
+
 /*
  * Local variables:
  * mode: C
diff --git a/xen/include/asm-x86/guest/hyperv-tlfs.h 
b/xen/include/asm-x86/guest/hyperv-tlfs.h
index 05c4044976..07db57b55f 100644
--- a/xen/include/asm-x86/guest/hyperv-tlfs.h
+++ b/xen/include/asm-x86/guest/hyperv-tlfs.h
@@ -318,15 +318,16 @@ struct ms_hyperv_tsc_page {
  *
  * Bit(s)
  * 63 - Indicates if the OS is Open Source or not; 1 is Open Source
- * 62:56 - Os Type; Linux is 0x100
+ * 62:56 - Os Type; Linux 0x1, FreeBSD 0x2, Xen 0x3
  * 55:48 - Distro specific identification
- * 47:16 - Linux kernel version number
+ * 47:16 - Guest OS version number
  * 15:0  - Distro specific identification
  *
  *
  */
 
 #define HV_LINUX_VENDOR_ID              0x8100
+#define HV_XEN_VENDOR_ID                0x8300
 union hv_guest_os_id
 {
     uint64_t raw;
diff --git a/xen/include/asm-x86/guest/hyperv.h 
b/xen/include/asm-x86/guest/hyperv.h
index c7a7f32bd5..0dcd8082ad 100644
--- a/xen/include/asm-x86/guest/hyperv.h
+++ b/xen/include/asm-x86/guest/hyperv.h
@@ -21,6 +21,9 @@
 
 #include <xen/types.h>
 
+/* Use top-most MFN for hypercall page */
+#define HV_HCALL_MFN (((1ull << paddr_bits) - 1) >> HV_HYP_PAGE_SHIFT)
+
 /*
  * The specification says: "The partition reference time is computed
  * by the following formula:
-- 
2.20.1


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