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[Xen-devel] [PATCH v7 05/10] x86/hyperv: setup hypercall page

Wei Liu posted 10 patches 6 years ago
[Xen-devel] [PATCH v7 05/10] x86/hyperv: setup hypercall page
Posted by Wei Liu 6 years ago 
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.

To avoid shattering L0 superpages and treading on any MMIO areas
residing in low addresses, use the top-most addressable page for that
purpose. Adjust e820 map 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@microsoft.com>
---
v7:
1. Fix a style issue
2. Initialise ID to 0
3. Update commit message

v6:
1. Use hv_guest_os_id
2. Use new e820_fixup hook
3. Add a BUILD_BUG_ON

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/guest/hyperv/hyperv.c      | 69 +++++++++++++++++++++++--
 xen/include/asm-x86/guest/hyperv-tlfs.h |  5 +-
 xen/include/asm-x86/guest/hyperv.h      |  3 ++
 3 files changed, 72 insertions(+), 5 deletions(-)

diff --git a/xen/arch/x86/guest/hyperv/hyperv.c b/xen/arch/x86/guest/hyperv/hyperv.c
index 8d38313d7a..2e20a96f30 100644
--- a/xen/arch/x86/guest/hyperv/hyperv.c
+++ b/xen/arch/x86/guest/hyperv/hyperv.c
@@ -19,15 +19,27 @@
  * 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)
+{
+    union hv_guest_os_id id = {};
+
+    id.vendor = HV_XEN_VENDOR_ID;
+    id.major = xen_major_version();
+    id.minor = xen_minor_version();
+
+    return id.raw;
+}
+
+static const struct hypervisor_ops ops;
 
 const struct hypervisor_ops *__init hyperv_probe(void)
 {
@@ -72,6 +84,57 @@ 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;
+
+    BUILD_BUG_ON(HV_HYP_PAGE_SHIFT != PAGE_SHIFT);
+
+    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 void __init e820_fixup(struct e820map *e820)
+{
+    uint64_t s = HV_HCALL_MFN << PAGE_SHIFT;
+
+    if ( !e820_add_range(e820, s, s + PAGE_SIZE, E820_RESERVED) )
+        panic("Unable to reserve Hyper-V hypercall range\n");
+}
+
+static const struct hypervisor_ops ops = {
+    .name = "Hyper-V",
+    .setup = setup,
+    .e820_fixup = e820_fixup,
+};
+
 /*
  * 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 091e25cdd1..0a0f3398c1 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..1a1b47831c 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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Re: [Xen-devel] [PATCH v7 05/10] x86/hyperv: setup hypercall page
Posted by Roger Pau Monné 6 years ago 
On Tue, Feb 04, 2020 at 03:36:59PM +0000, Wei Liu wrote:
> 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.
> 
> To avoid shattering L0 superpages and treading on any MMIO areas
> residing in low addresses, use the top-most addressable page for that
> purpose. Adjust e820 map 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@microsoft.com>

Reviewed-by: Roger Pau Monné <roger.pau@citrix.com>

> ---
> v7:
> 1. Fix a style issue
> 2. Initialise ID to 0
> 3. Update commit message
> 
> v6:
> 1. Use hv_guest_os_id
> 2. Use new e820_fixup hook
> 3. Add a BUILD_BUG_ON
> 
> 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/guest/hyperv/hyperv.c      | 69 +++++++++++++++++++++++--
>  xen/include/asm-x86/guest/hyperv-tlfs.h |  5 +-
>  xen/include/asm-x86/guest/hyperv.h      |  3 ++
>  3 files changed, 72 insertions(+), 5 deletions(-)
> 
> diff --git a/xen/arch/x86/guest/hyperv/hyperv.c b/xen/arch/x86/guest/hyperv/hyperv.c
> index 8d38313d7a..2e20a96f30 100644
> --- a/xen/arch/x86/guest/hyperv/hyperv.c
> +++ b/xen/arch/x86/guest/hyperv/hyperv.c
> @@ -19,15 +19,27 @@
>   * 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)
> +{
> +    union hv_guest_os_id id = {};
> +
> +    id.vendor = HV_XEN_VENDOR_ID;
> +    id.major = xen_major_version();
> +    id.minor = xen_minor_version();
> +
> +    return id.raw;
> +}
> +
> +static const struct hypervisor_ops ops;
>  
>  const struct hypervisor_ops *__init hyperv_probe(void)
>  {
> @@ -72,6 +84,57 @@ 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;
> +
> +    BUILD_BUG_ON(HV_HYP_PAGE_SHIFT != PAGE_SHIFT);
> +
> +    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;

Is it expected that the guest ID or the hypercal page is already
setup?

Ie: would virtual firmware setup any of this? (and not clean it up
afterwards)

Thanks, Roger.

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Re: [Xen-devel] [PATCH v7 05/10] x86/hyperv: setup hypercall page
Posted by Wei Liu 6 years ago 
On Wed, Feb 05, 2020 at 03:04:16PM +0100, Roger Pau Monné wrote:
[...]
> > +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;
> > +
> > +    BUILD_BUG_ON(HV_HYP_PAGE_SHIFT != PAGE_SHIFT);
> > +
> > +    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;
> 
> Is it expected that the guest ID or the hypercal page is already
> setup?
> 
> Ie: would virtual firmware setup any of this? (and not clean it up
> afterwards)

There is no definitive answer to why/when this happens in TLFS, but it
does require guest to respect that is already in the MSR.

Wei.

> 
> Thanks, Roger.

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Re: [Xen-devel] [PATCH v7 05/10] x86/hyperv: setup hypercall page
Posted by Wei Liu 6 years ago 
On Wed, Feb 05, 2020 at 03:00:24PM +0000, Wei Liu wrote:
> On Wed, Feb 05, 2020 at 03:04:16PM +0100, Roger Pau Monné wrote:
> [...]
> > > +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;
> > > +
> > > +    BUILD_BUG_ON(HV_HYP_PAGE_SHIFT != PAGE_SHIFT);
> > > +
> > > +    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;
> > 
> > Is it expected that the guest ID or the hypercal page is already
> > setup?
> > 
> > Ie: would virtual firmware setup any of this? (and not clean it up
> > afterwards)
> 
> There is no definitive answer to why/when this happens in TLFS, but it
> does require guest to respect that is already in the MSR.

My guess would be after migration Hyper-V sets up the same MSR/page
FWIW.

Wei.

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