diff mbox

[RFC,06/14] OvmfPkg/XenPlatformPei: Add xen PVH specific code

Message ID 20161208153340.2285-7-anthony.perard@citrix.com (mailing list archive)
State New, archived
Headers show

Commit Message

Anthony PERARD Dec. 8, 2016, 3:33 p.m. UTC
- learn about memory size from the E820
- ignore error if host bridge devid is 0xffff, PVH does not have PCI and
  reading from unexisting device return -1.

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Anthony PERARD <anthony.perard@citrix.com>
---
 OvmfPkg/XenPlatformPei/MemDetect.c | 71 ++++++++++++++++++++++++++++++++++++++
 OvmfPkg/XenPlatformPei/Platform.c  |  5 +++
 OvmfPkg/XenPlatformPei/Platform.h  | 10 ++++++
 3 files changed, 86 insertions(+)

Comments

Laszlo Ersek Jan. 5, 2017, 10:30 a.m. UTC | #1
On 12/08/16 16:33, Anthony PERARD wrote:
> - learn about memory size from the E820
> - ignore error if host bridge devid is 0xffff, PVH does not have PCI and
>   reading from unexisting device return -1.
> 
> Contributed-under: TianoCore Contribution Agreement 1.0
> Signed-off-by: Anthony PERARD <anthony.perard@citrix.com>
> ---
>  OvmfPkg/XenPlatformPei/MemDetect.c | 71 ++++++++++++++++++++++++++++++++++++++
>  OvmfPkg/XenPlatformPei/Platform.c  |  5 +++
>  OvmfPkg/XenPlatformPei/Platform.h  | 10 ++++++
>  3 files changed, 86 insertions(+)
> 
> diff --git a/OvmfPkg/XenPlatformPei/MemDetect.c b/OvmfPkg/XenPlatformPei/MemDetect.c
> index 4ecdf5e..0d80775 100644
> --- a/OvmfPkg/XenPlatformPei/MemDetect.c
> +++ b/OvmfPkg/XenPlatformPei/MemDetect.c
> @@ -42,6 +42,70 @@ UINT8 mPhysMemAddressWidth;
>  STATIC UINT32 mS3AcpiReservedMemoryBase;
>  STATIC UINT32 mS3AcpiReservedMemorySize;
>  
> +STATIC UINT32 mXenLowerMemorySize = 0;
> +STATIC UINT64 mXenHighMemorySize = 0;
> +
> +VOID
> +XenReadMemorySizes (
> +  VOID
> +  )
> +{
> +  EFI_E820_ENTRY64  *E820Map;
> +  UINT32            E820EntriesCount;
> +  EFI_STATUS Status;
> +
> +  Status = XenGetE820Map (&E820Map, &E820EntriesCount);
> +  ASSERT_EFI_ERROR (Status);
> +
> +  mXenLowerMemorySize = 0;
> +  mXenHighMemorySize = 0;
> +
> +  if (E820EntriesCount > 0) {
> +    EFI_E820_ENTRY64 *Entry;
> +    UINT32 Loop;
> +
> +    for (Loop = 0; Loop < E820EntriesCount; Loop++) {
> +      Entry = E820Map + Loop;
> +
> +      //
> +      // Only care about RAM
> +      //
> +      if (Entry->Type != EfiAcpiAddressRangeMemory) {
> +        continue;
> +      }
> +
> +      if ((Entry->BaseAddr + Entry->Length) <= SIZE_16MB) {
> +        continue;
> +      }
> +
> +      if (Entry->BaseAddr < SIZE_16MB) {
> +        UINT64 bottom = Entry->BaseAddr;
> +        UINT64 size = Entry->Length;
> +        size -= SIZE_16MB - bottom;
> +        bottom = SIZE_16MB;
> +        mXenLowerMemorySize += size;
> +        continue;
> +      }
> +      if (Entry->BaseAddr <= SIZE_4GB) {
> +        UINT64 size = Entry->Length;
> +        mXenLowerMemorySize += size;
> +        continue;
> +      }
> +
> +      if (Entry->BaseAddr == SIZE_4GB) {
> +        mXenHighMemorySize = Entry->Length;
> +        continue;
> +      }
> +
> +      DEBUG ((EFI_D_INFO, "%a: ignored XenE820 entry (0x%llx, 0x%llx)\n",
> +              __FUNCTION__,
> +              Entry->BaseAddr,
> +              Entry->Length));
> +    }
> +    mXenLowerMemorySize += SIZE_16MB;
> +  }
> +}
> +
>  UINT32
>  GetSystemMemorySizeBelow4gb (
>    VOID
> @@ -50,6 +114,9 @@ GetSystemMemorySizeBelow4gb (
>    UINT8 Cmos0x34;
>    UINT8 Cmos0x35;
>  
> +  if (mXen && mXenLowerMemorySize)
> +    return mXenLowerMemorySize;
> +
>    //
>    // CMOS 0x34/0x35 specifies the system memory above 16 MB.
>    // * CMOS(0x35) is the high byte
> @@ -74,6 +141,10 @@ GetSystemMemorySizeAbove4gb (
>    UINT32 Size;
>    UINTN  CmosIndex;
>  
> +  // if lower memory is specified that way, return also high memory
> +  if (mXen && mXenLowerMemorySize)
> +    return mXenHighMemorySize;
> +
>    //
>    // CMOS 0x5b-0x5d specifies the system memory above 4GB MB.
>    // * CMOS(0x5d) is the most significant size byte
> diff --git a/OvmfPkg/XenPlatformPei/Platform.c b/OvmfPkg/XenPlatformPei/Platform.c
> index bf78878..9fc713c 100644
> --- a/OvmfPkg/XenPlatformPei/Platform.c
> +++ b/OvmfPkg/XenPlatformPei/Platform.c
> @@ -362,6 +362,10 @@ MiscInitialization (
>        AcpiCtlReg = POWER_MGMT_REGISTER_Q35 (ICH9_ACPI_CNTL);
>        AcpiEnBit  = ICH9_ACPI_CNTL_ACPI_EN;
>        break;
> +    case 0xffff:
> +      // xen PVH, ignore
> +      PcdStatus = PcdSet16S (PcdOvmfHostBridgePciDevId, mHostBridgeDevId);
> +      return;

Can we create a new macro for 0xFFFF in
"OvmfPkg/Include/OvmfPlatforms.h", and use that here?

Normally I would suggest a separate header file under "OvmfPkg/Include",
similar to "Q35MchIch9.h" and "I440FxPiix4.h", and to include that new
file in "OvmfPlatforms.h", but here we only need a single "chipset
identifier", so I guess that can go directly into "OvmfPlatforms.h".

I mainly suggest this because in patch 08/14, the same 0xFFFF case label
is being added to code shared with QEMU, and using a verbose macro there
is much better than a magic number. In turn, we should use the same
macro here, I think.

Looks OK otherwise.

Thanks
Laszlo

>      default:
>        DEBUG ((EFI_D_ERROR, "%a: Unknown Host Bridge Device ID: 0x%04x\n",
>          __FUNCTION__, mHostBridgeDevId));
> @@ -503,6 +507,7 @@ InitializeXenPlatform (
>    DebugDumpCmos ();
>  
>    XenDetect ();
> +  XenReadMemorySizes ();
>  
>    BootModeInitialization ();
>    AddressWidthInitialization ();
> diff --git a/OvmfPkg/XenPlatformPei/Platform.h b/OvmfPkg/XenPlatformPei/Platform.h
> index eda765b..2948853 100644
> --- a/OvmfPkg/XenPlatformPei/Platform.h
> +++ b/OvmfPkg/XenPlatformPei/Platform.h
> @@ -101,4 +101,14 @@ extern BOOLEAN mS3Supported;
>  
>  extern UINT8 mPhysMemAddressWidth;
>  
> +EFI_STATUS
> +XenGetE820Map (
> +  EFI_E820_ENTRY64 **Entries,
> +  UINT32 *Count
> +  );
> +VOID
> +XenReadMemorySizes (
> +  VOID
> +  );
> +
>  #endif // _PLATFORM_PEI_H_INCLUDED_
>
Anthony PERARD Jan. 10, 2017, 4:18 p.m. UTC | #2
On Thu, Jan 05, 2017 at 11:30:32AM +0100, Laszlo Ersek wrote:
> On 12/08/16 16:33, Anthony PERARD wrote:
> > - learn about memory size from the E820
> > - ignore error if host bridge devid is 0xffff, PVH does not have PCI and
> >   reading from unexisting device return -1.
> > 
> > Contributed-under: TianoCore Contribution Agreement 1.0
> > Signed-off-by: Anthony PERARD <anthony.perard@citrix.com>
> > ---
> >  OvmfPkg/XenPlatformPei/MemDetect.c | 71 ++++++++++++++++++++++++++++++++++++++
> >  OvmfPkg/XenPlatformPei/Platform.c  |  5 +++
> >  OvmfPkg/XenPlatformPei/Platform.h  | 10 ++++++
> >  3 files changed, 86 insertions(+)
> > 
> > diff --git a/OvmfPkg/XenPlatformPei/MemDetect.c b/OvmfPkg/XenPlatformPei/MemDetect.c
> > index 4ecdf5e..0d80775 100644
> > --- a/OvmfPkg/XenPlatformPei/MemDetect.c
> > +++ b/OvmfPkg/XenPlatformPei/MemDetect.c
> > @@ -42,6 +42,70 @@ UINT8 mPhysMemAddressWidth;
> >  STATIC UINT32 mS3AcpiReservedMemoryBase;
> >  STATIC UINT32 mS3AcpiReservedMemorySize;
> >  
> > +STATIC UINT32 mXenLowerMemorySize = 0;
> > +STATIC UINT64 mXenHighMemorySize = 0;
> > +
> > +VOID
> > +XenReadMemorySizes (
> > +  VOID
> > +  )
> > +{
> > +  EFI_E820_ENTRY64  *E820Map;
> > +  UINT32            E820EntriesCount;
> > +  EFI_STATUS Status;
> > +
> > +  Status = XenGetE820Map (&E820Map, &E820EntriesCount);
> > +  ASSERT_EFI_ERROR (Status);
> > +
> > +  mXenLowerMemorySize = 0;
> > +  mXenHighMemorySize = 0;
> > +
> > +  if (E820EntriesCount > 0) {
> > +    EFI_E820_ENTRY64 *Entry;
> > +    UINT32 Loop;
> > +
> > +    for (Loop = 0; Loop < E820EntriesCount; Loop++) {
> > +      Entry = E820Map + Loop;
> > +
> > +      //
> > +      // Only care about RAM
> > +      //
> > +      if (Entry->Type != EfiAcpiAddressRangeMemory) {
> > +        continue;
> > +      }
> > +
> > +      if ((Entry->BaseAddr + Entry->Length) <= SIZE_16MB) {
> > +        continue;
> > +      }
> > +
> > +      if (Entry->BaseAddr < SIZE_16MB) {
> > +        UINT64 bottom = Entry->BaseAddr;
> > +        UINT64 size = Entry->Length;
> > +        size -= SIZE_16MB - bottom;
> > +        bottom = SIZE_16MB;
> > +        mXenLowerMemorySize += size;
> > +        continue;
> > +      }
> > +      if (Entry->BaseAddr <= SIZE_4GB) {
> > +        UINT64 size = Entry->Length;
> > +        mXenLowerMemorySize += size;
> > +        continue;
> > +      }
> > +
> > +      if (Entry->BaseAddr == SIZE_4GB) {
> > +        mXenHighMemorySize = Entry->Length;
> > +        continue;
> > +      }
> > +
> > +      DEBUG ((EFI_D_INFO, "%a: ignored XenE820 entry (0x%llx, 0x%llx)\n",
> > +              __FUNCTION__,
> > +              Entry->BaseAddr,
> > +              Entry->Length));
> > +    }
> > +    mXenLowerMemorySize += SIZE_16MB;
> > +  }
> > +}
> > +
> >  UINT32
> >  GetSystemMemorySizeBelow4gb (
> >    VOID
> > @@ -50,6 +114,9 @@ GetSystemMemorySizeBelow4gb (
> >    UINT8 Cmos0x34;
> >    UINT8 Cmos0x35;
> >  
> > +  if (mXen && mXenLowerMemorySize)
> > +    return mXenLowerMemorySize;
> > +
> >    //
> >    // CMOS 0x34/0x35 specifies the system memory above 16 MB.
> >    // * CMOS(0x35) is the high byte
> > @@ -74,6 +141,10 @@ GetSystemMemorySizeAbove4gb (
> >    UINT32 Size;
> >    UINTN  CmosIndex;
> >  
> > +  // if lower memory is specified that way, return also high memory
> > +  if (mXen && mXenLowerMemorySize)
> > +    return mXenHighMemorySize;
> > +
> >    //
> >    // CMOS 0x5b-0x5d specifies the system memory above 4GB MB.
> >    // * CMOS(0x5d) is the most significant size byte
> > diff --git a/OvmfPkg/XenPlatformPei/Platform.c b/OvmfPkg/XenPlatformPei/Platform.c
> > index bf78878..9fc713c 100644
> > --- a/OvmfPkg/XenPlatformPei/Platform.c
> > +++ b/OvmfPkg/XenPlatformPei/Platform.c
> > @@ -362,6 +362,10 @@ MiscInitialization (
> >        AcpiCtlReg = POWER_MGMT_REGISTER_Q35 (ICH9_ACPI_CNTL);
> >        AcpiEnBit  = ICH9_ACPI_CNTL_ACPI_EN;
> >        break;
> > +    case 0xffff:
> > +      // xen PVH, ignore
> > +      PcdStatus = PcdSet16S (PcdOvmfHostBridgePciDevId, mHostBridgeDevId);
> > +      return;
> 
> Can we create a new macro for 0xFFFF in
> "OvmfPkg/Include/OvmfPlatforms.h", and use that here?
> 
> Normally I would suggest a separate header file under "OvmfPkg/Include",
> similar to "Q35MchIch9.h" and "I440FxPiix4.h", and to include that new
> file in "OvmfPlatforms.h", but here we only need a single "chipset
> identifier", so I guess that can go directly into "OvmfPlatforms.h".
> 
> I mainly suggest this because in patch 08/14, the same 0xFFFF case label
> is being added to code shared with QEMU, and using a verbose macro there
> is much better than a magic number. In turn, we should use the same
> macro here, I think.

This value is just the result of a read to an incorrect location, and
the return value is -1. There is no PCI when running in Xen PVH, at
least for now. I think I should try harder to find out if OVMF is
running in PVH, and so I would not need this case 0xffff at all.
Laszlo Ersek Jan. 10, 2017, 4:54 p.m. UTC | #3
On 01/10/17 17:18, Anthony PERARD wrote:
> On Thu, Jan 05, 2017 at 11:30:32AM +0100, Laszlo Ersek wrote:
>> On 12/08/16 16:33, Anthony PERARD wrote:
>>> - learn about memory size from the E820
>>> - ignore error if host bridge devid is 0xffff, PVH does not have PCI and
>>>   reading from unexisting device return -1.
>>>
>>> Contributed-under: TianoCore Contribution Agreement 1.0
>>> Signed-off-by: Anthony PERARD <anthony.perard@citrix.com>
>>> ---
>>>  OvmfPkg/XenPlatformPei/MemDetect.c | 71 ++++++++++++++++++++++++++++++++++++++
>>>  OvmfPkg/XenPlatformPei/Platform.c  |  5 +++
>>>  OvmfPkg/XenPlatformPei/Platform.h  | 10 ++++++
>>>  3 files changed, 86 insertions(+)
>>>
>>> diff --git a/OvmfPkg/XenPlatformPei/MemDetect.c b/OvmfPkg/XenPlatformPei/MemDetect.c
>>> index 4ecdf5e..0d80775 100644
>>> --- a/OvmfPkg/XenPlatformPei/MemDetect.c
>>> +++ b/OvmfPkg/XenPlatformPei/MemDetect.c
>>> @@ -42,6 +42,70 @@ UINT8 mPhysMemAddressWidth;
>>>  STATIC UINT32 mS3AcpiReservedMemoryBase;
>>>  STATIC UINT32 mS3AcpiReservedMemorySize;
>>>  
>>> +STATIC UINT32 mXenLowerMemorySize = 0;
>>> +STATIC UINT64 mXenHighMemorySize = 0;
>>> +
>>> +VOID
>>> +XenReadMemorySizes (
>>> +  VOID
>>> +  )
>>> +{
>>> +  EFI_E820_ENTRY64  *E820Map;
>>> +  UINT32            E820EntriesCount;
>>> +  EFI_STATUS Status;
>>> +
>>> +  Status = XenGetE820Map (&E820Map, &E820EntriesCount);
>>> +  ASSERT_EFI_ERROR (Status);
>>> +
>>> +  mXenLowerMemorySize = 0;
>>> +  mXenHighMemorySize = 0;
>>> +
>>> +  if (E820EntriesCount > 0) {
>>> +    EFI_E820_ENTRY64 *Entry;
>>> +    UINT32 Loop;
>>> +
>>> +    for (Loop = 0; Loop < E820EntriesCount; Loop++) {
>>> +      Entry = E820Map + Loop;
>>> +
>>> +      //
>>> +      // Only care about RAM
>>> +      //
>>> +      if (Entry->Type != EfiAcpiAddressRangeMemory) {
>>> +        continue;
>>> +      }
>>> +
>>> +      if ((Entry->BaseAddr + Entry->Length) <= SIZE_16MB) {
>>> +        continue;
>>> +      }
>>> +
>>> +      if (Entry->BaseAddr < SIZE_16MB) {
>>> +        UINT64 bottom = Entry->BaseAddr;
>>> +        UINT64 size = Entry->Length;
>>> +        size -= SIZE_16MB - bottom;
>>> +        bottom = SIZE_16MB;
>>> +        mXenLowerMemorySize += size;
>>> +        continue;
>>> +      }
>>> +      if (Entry->BaseAddr <= SIZE_4GB) {
>>> +        UINT64 size = Entry->Length;
>>> +        mXenLowerMemorySize += size;
>>> +        continue;
>>> +      }
>>> +
>>> +      if (Entry->BaseAddr == SIZE_4GB) {
>>> +        mXenHighMemorySize = Entry->Length;
>>> +        continue;
>>> +      }
>>> +
>>> +      DEBUG ((EFI_D_INFO, "%a: ignored XenE820 entry (0x%llx, 0x%llx)\n",
>>> +              __FUNCTION__,
>>> +              Entry->BaseAddr,
>>> +              Entry->Length));
>>> +    }
>>> +    mXenLowerMemorySize += SIZE_16MB;
>>> +  }
>>> +}
>>> +
>>>  UINT32
>>>  GetSystemMemorySizeBelow4gb (
>>>    VOID
>>> @@ -50,6 +114,9 @@ GetSystemMemorySizeBelow4gb (
>>>    UINT8 Cmos0x34;
>>>    UINT8 Cmos0x35;
>>>  
>>> +  if (mXen && mXenLowerMemorySize)
>>> +    return mXenLowerMemorySize;
>>> +
>>>    //
>>>    // CMOS 0x34/0x35 specifies the system memory above 16 MB.
>>>    // * CMOS(0x35) is the high byte
>>> @@ -74,6 +141,10 @@ GetSystemMemorySizeAbove4gb (
>>>    UINT32 Size;
>>>    UINTN  CmosIndex;
>>>  
>>> +  // if lower memory is specified that way, return also high memory
>>> +  if (mXen && mXenLowerMemorySize)
>>> +    return mXenHighMemorySize;
>>> +
>>>    //
>>>    // CMOS 0x5b-0x5d specifies the system memory above 4GB MB.
>>>    // * CMOS(0x5d) is the most significant size byte
>>> diff --git a/OvmfPkg/XenPlatformPei/Platform.c b/OvmfPkg/XenPlatformPei/Platform.c
>>> index bf78878..9fc713c 100644
>>> --- a/OvmfPkg/XenPlatformPei/Platform.c
>>> +++ b/OvmfPkg/XenPlatformPei/Platform.c
>>> @@ -362,6 +362,10 @@ MiscInitialization (
>>>        AcpiCtlReg = POWER_MGMT_REGISTER_Q35 (ICH9_ACPI_CNTL);
>>>        AcpiEnBit  = ICH9_ACPI_CNTL_ACPI_EN;
>>>        break;
>>> +    case 0xffff:
>>> +      // xen PVH, ignore
>>> +      PcdStatus = PcdSet16S (PcdOvmfHostBridgePciDevId, mHostBridgeDevId);
>>> +      return;
>>
>> Can we create a new macro for 0xFFFF in
>> "OvmfPkg/Include/OvmfPlatforms.h", and use that here?
>>
>> Normally I would suggest a separate header file under "OvmfPkg/Include",
>> similar to "Q35MchIch9.h" and "I440FxPiix4.h", and to include that new
>> file in "OvmfPlatforms.h", but here we only need a single "chipset
>> identifier", so I guess that can go directly into "OvmfPlatforms.h".
>>
>> I mainly suggest this because in patch 08/14, the same 0xFFFF case label
>> is being added to code shared with QEMU, and using a verbose macro there
>> is much better than a magic number. In turn, we should use the same
>> macro here, I think.
> 
> This value is just the result of a read to an incorrect location, and
> the return value is -1. There is no PCI when running in Xen PVH, at
> least for now. I think I should try harder to find out if OVMF is
> running in PVH, and so I would not need this case 0xffff at all.
> 

Right, that would be best.

In fact, this affects two modules, (Xen)PlatformPei and
PlatformBootManagerLib. In both, we already have the XenDetected()
function. Maybe you can add a XenPvhDetected() function as well (which
would return TRUE only for PVH, while the original XenDetected() would
continue returning TRUE for both HVM and PVH). Then the PCI host bridge
ID checking could be entirely short-circuited if XenPvhDetected()
returned TRUE first.

Thanks
Laszlo
Roger Pau Monne Jan. 10, 2017, 6:36 p.m. UTC | #4
On Tue, Jan 10, 2017 at 05:54:49PM +0100, Laszlo Ersek wrote:
> On 01/10/17 17:18, Anthony PERARD wrote:
> > On Thu, Jan 05, 2017 at 11:30:32AM +0100, Laszlo Ersek wrote:
> >> On 12/08/16 16:33, Anthony PERARD wrote:
> >>> diff --git a/OvmfPkg/XenPlatformPei/Platform.c b/OvmfPkg/XenPlatformPei/Platform.c
> >>> index bf78878..9fc713c 100644
> >>> --- a/OvmfPkg/XenPlatformPei/Platform.c
> >>> +++ b/OvmfPkg/XenPlatformPei/Platform.c
> >>> @@ -362,6 +362,10 @@ MiscInitialization (
> >>>        AcpiCtlReg = POWER_MGMT_REGISTER_Q35 (ICH9_ACPI_CNTL);
> >>>        AcpiEnBit  = ICH9_ACPI_CNTL_ACPI_EN;
> >>>        break;
> >>> +    case 0xffff:
> >>> +      // xen PVH, ignore
> >>> +      PcdStatus = PcdSet16S (PcdOvmfHostBridgePciDevId, mHostBridgeDevId);
> >>> +      return;
> >>
> >> Can we create a new macro for 0xFFFF in
> >> "OvmfPkg/Include/OvmfPlatforms.h", and use that here?
> >>
> >> Normally I would suggest a separate header file under "OvmfPkg/Include",
> >> similar to "Q35MchIch9.h" and "I440FxPiix4.h", and to include that new
> >> file in "OvmfPlatforms.h", but here we only need a single "chipset
> >> identifier", so I guess that can go directly into "OvmfPlatforms.h".
> >>
> >> I mainly suggest this because in patch 08/14, the same 0xFFFF case label
> >> is being added to code shared with QEMU, and using a verbose macro there
> >> is much better than a magic number. In turn, we should use the same
> >> macro here, I think.
> > 
> > This value is just the result of a read to an incorrect location, and
> > the return value is -1. There is no PCI when running in Xen PVH, at
> > least for now. I think I should try harder to find out if OVMF is
> > running in PVH, and so I would not need this case 0xffff at all.
> > 
> 
> Right, that would be best.
> 
> In fact, this affects two modules, (Xen)PlatformPei and
> PlatformBootManagerLib. In both, we already have the XenDetected()
> function. Maybe you can add a XenPvhDetected() function as well (which
> would return TRUE only for PVH, while the original XenDetected() would
> continue returning TRUE for both HVM and PVH). Then the PCI host bridge
> ID checking could be entirely short-circuited if XenPvhDetected()
> returned TRUE first.

It's very likely that when doing PCI-passthrough to a PVH guest an emulated
PCI host bridge is going to be available, so short-circuiting the bridge check
just based on PVH detection would then be wrong.

Roger.
diff mbox

Patch

diff --git a/OvmfPkg/XenPlatformPei/MemDetect.c b/OvmfPkg/XenPlatformPei/MemDetect.c
index 4ecdf5e..0d80775 100644
--- a/OvmfPkg/XenPlatformPei/MemDetect.c
+++ b/OvmfPkg/XenPlatformPei/MemDetect.c
@@ -42,6 +42,70 @@  UINT8 mPhysMemAddressWidth;
 STATIC UINT32 mS3AcpiReservedMemoryBase;
 STATIC UINT32 mS3AcpiReservedMemorySize;
 
+STATIC UINT32 mXenLowerMemorySize = 0;
+STATIC UINT64 mXenHighMemorySize = 0;
+
+VOID
+XenReadMemorySizes (
+  VOID
+  )
+{
+  EFI_E820_ENTRY64  *E820Map;
+  UINT32            E820EntriesCount;
+  EFI_STATUS Status;
+
+  Status = XenGetE820Map (&E820Map, &E820EntriesCount);
+  ASSERT_EFI_ERROR (Status);
+
+  mXenLowerMemorySize = 0;
+  mXenHighMemorySize = 0;
+
+  if (E820EntriesCount > 0) {
+    EFI_E820_ENTRY64 *Entry;
+    UINT32 Loop;
+
+    for (Loop = 0; Loop < E820EntriesCount; Loop++) {
+      Entry = E820Map + Loop;
+
+      //
+      // Only care about RAM
+      //
+      if (Entry->Type != EfiAcpiAddressRangeMemory) {
+        continue;
+      }
+
+      if ((Entry->BaseAddr + Entry->Length) <= SIZE_16MB) {
+        continue;
+      }
+
+      if (Entry->BaseAddr < SIZE_16MB) {
+        UINT64 bottom = Entry->BaseAddr;
+        UINT64 size = Entry->Length;
+        size -= SIZE_16MB - bottom;
+        bottom = SIZE_16MB;
+        mXenLowerMemorySize += size;
+        continue;
+      }
+      if (Entry->BaseAddr <= SIZE_4GB) {
+        UINT64 size = Entry->Length;
+        mXenLowerMemorySize += size;
+        continue;
+      }
+
+      if (Entry->BaseAddr == SIZE_4GB) {
+        mXenHighMemorySize = Entry->Length;
+        continue;
+      }
+
+      DEBUG ((EFI_D_INFO, "%a: ignored XenE820 entry (0x%llx, 0x%llx)\n",
+              __FUNCTION__,
+              Entry->BaseAddr,
+              Entry->Length));
+    }
+    mXenLowerMemorySize += SIZE_16MB;
+  }
+}
+
 UINT32
 GetSystemMemorySizeBelow4gb (
   VOID
@@ -50,6 +114,9 @@  GetSystemMemorySizeBelow4gb (
   UINT8 Cmos0x34;
   UINT8 Cmos0x35;
 
+  if (mXen && mXenLowerMemorySize)
+    return mXenLowerMemorySize;
+
   //
   // CMOS 0x34/0x35 specifies the system memory above 16 MB.
   // * CMOS(0x35) is the high byte
@@ -74,6 +141,10 @@  GetSystemMemorySizeAbove4gb (
   UINT32 Size;
   UINTN  CmosIndex;
 
+  // if lower memory is specified that way, return also high memory
+  if (mXen && mXenLowerMemorySize)
+    return mXenHighMemorySize;
+
   //
   // CMOS 0x5b-0x5d specifies the system memory above 4GB MB.
   // * CMOS(0x5d) is the most significant size byte
diff --git a/OvmfPkg/XenPlatformPei/Platform.c b/OvmfPkg/XenPlatformPei/Platform.c
index bf78878..9fc713c 100644
--- a/OvmfPkg/XenPlatformPei/Platform.c
+++ b/OvmfPkg/XenPlatformPei/Platform.c
@@ -362,6 +362,10 @@  MiscInitialization (
       AcpiCtlReg = POWER_MGMT_REGISTER_Q35 (ICH9_ACPI_CNTL);
       AcpiEnBit  = ICH9_ACPI_CNTL_ACPI_EN;
       break;
+    case 0xffff:
+      // xen PVH, ignore
+      PcdStatus = PcdSet16S (PcdOvmfHostBridgePciDevId, mHostBridgeDevId);
+      return;
     default:
       DEBUG ((EFI_D_ERROR, "%a: Unknown Host Bridge Device ID: 0x%04x\n",
         __FUNCTION__, mHostBridgeDevId));
@@ -503,6 +507,7 @@  InitializeXenPlatform (
   DebugDumpCmos ();
 
   XenDetect ();
+  XenReadMemorySizes ();
 
   BootModeInitialization ();
   AddressWidthInitialization ();
diff --git a/OvmfPkg/XenPlatformPei/Platform.h b/OvmfPkg/XenPlatformPei/Platform.h
index eda765b..2948853 100644
--- a/OvmfPkg/XenPlatformPei/Platform.h
+++ b/OvmfPkg/XenPlatformPei/Platform.h
@@ -101,4 +101,14 @@  extern BOOLEAN mS3Supported;
 
 extern UINT8 mPhysMemAddressWidth;
 
+EFI_STATUS
+XenGetE820Map (
+  EFI_E820_ENTRY64 **Entries,
+  UINT32 *Count
+  );
+VOID
+XenReadMemorySizes (
+  VOID
+  );
+
 #endif // _PLATFORM_PEI_H_INCLUDED_