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Add support for running UEFI without VMBus #76

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edd7ad0
Add support for running UEFI without VMBus
jstarks May 15, 2026
86b41fd
feedback
jstarks May 15, 2026
4a6809d
Make MMIO blob always required; high MMIO optional by size
jstarks May 18, 2026
2001333
Fix no high MMIO and quiet vmbus noise
jstarks May 21, 2026
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1 change: 1 addition & 0 deletions MsvmPkg/AcpiPlatformDxe/AcpiPlatformDxe.inf
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Original file line number Diff line number Diff line change
Expand Up @@ -95,6 +95,7 @@
gMsvmPkgTokenSpaceGuid.PcdHmatSize ## CONSUMES
gMsvmPkgTokenSpaceGuid.PcdTpmEnabled ## CONSUMES
gMsvmPkgTokenSpaceGuid.PcdVirtualBatteryEnabled ## CONSUMES
gMsvmPkgTokenSpaceGuid.PcdVmbusEnabled ## CONSUMES
gMsvmPkgTokenSpaceGuid.PcdWatchdogEnabled ## CONSUMES

[Pcd.X64]
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2 changes: 2 additions & 0 deletions MsvmPkg/AcpiPlatformDxe/Dsdt.c
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Expand Up @@ -33,6 +33,7 @@ typedef struct _DSDT_AML_DATA
UINT8 ProcIdleEnabled;
UINT8 CxlMemoryEnabled;
UINT16 NvdimmCount;
UINT8 VmbusEnabled;
} DSDT_AML_DATA;

typedef struct _DSDT_AML_DESCRIPTOR
Expand Down Expand Up @@ -138,6 +139,7 @@ Return Value:
data->ProcIdleEnabled = PcdGetBool(PcdProcIdleEnabled);
data->CxlMemoryEnabled = PcdGetBool(PcdCxlMemoryEnabled);
data->NvdimmCount = PcdGet16(PcdNvdimmCount);
data->VmbusEnabled = PcdGetBool(PcdVmbusEnabled);

DEBUG((DEBUG_VERBOSE, "--- %a: Mmio1Start 0x%lx\n", __func__, data->Mmio1Start));
DEBUG((DEBUG_VERBOSE, "--- %a: Mmio1Length 0x%lx\n", __func__, data->Mmio1Length));
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149 changes: 81 additions & 68 deletions MsvmPkg/AcpiTables/Dsdt.asl
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Expand Up @@ -63,6 +63,7 @@ DefinitionBlock (
PADE,8, // Processor Aggregator Device enabled/disabled
CCFG,8, // CXL memory support enabled/disabled
NCNT,16, // NVDIMM count
VCFG,8, // VMBus enabled/disabled
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}

// Supported machine sleep states =========================================
Expand Down Expand Up @@ -140,6 +141,7 @@ DefinitionBlock (
{
Name(_HID, "ACPI0004")
Name(_UID, 0)

Name(_CRS,
ResourceTemplate()
{
Expand All @@ -166,19 +168,27 @@ DefinitionBlock (

Method(_INI, 0)
{
// Update the DWORDMemory resource descriptor with the low MMIO region.
Store(MG2B, MIN6)
Store(MG2L, LEN6)
Store(MG2L, Local0)
Add(MIN6, Decrement(Local0), MAX6)
// Update the DWORDMemory descriptor with the low MMIO region
// only if the region has nonzero size.
If(LGreater(MG2L, 0))
{
Store(MG2B, MIN6)
Store(MG2L, LEN6)
Store(MG2L, Local0)
Add(MIN6, Decrement(Local0), MAX6)
}

// Update the QWORDMemory resource descriptor with the high MMIO region.
ShiftLeft (HMIB, 20, Local1)
ShiftLeft (HMIL, 20, Local2)
Store(Local1, MIN7)
Store(Local2, LEN7)
Store(Local2, Local0)
Add(MIN7, Decrement(Local0), MAX7)
// Update the QWORDMemory descriptor with the high MMIO region
// only if the region has nonzero size.
If(LGreater(HMIL, 0))
{
ShiftLeft (HMIB, 20, Local1)
ShiftLeft (HMIL, 20, Local2)
Store(Local1, MIN7)
Store(Local2, LEN7)
Store(Local2, Local0)
Add(MIN7, Decrement(Local0), MAX7)
}
}
}

Expand Down Expand Up @@ -306,74 +316,77 @@ DefinitionBlock (

// VMBus ==================================================================

Device(\_SB.VMOD.VMBS)
If(LGreater(VCFG, 0))
{
Name(STA, 0xF)
Name(_ADR, 0x00)
Device(\_SB.VMOD.VMBS)
{
Name(STA, 0xF)
Name(_ADR, 0x00)
#if defined(_DSDT_ARM_)
Name(_CCA, One)
Name(_CCA, One)
#endif
Name(_DDN, "VMBUS")
Name(_HID, "MSFT1000")
Name(_CID, "VMBus")
Name(_UID, 0)
Method(_DIS, 0) { And(STA, 0xD, STA) }
Method(_PS0, 0) { Or(STA, 0xF, STA) }
Method(_STA, 0)
{
return(STA)
}

// Older versions of this DSDT implemented _PS3 improperly, as:
// Name(_PS3, 0)
// This is intentionally a do-nothing method in case any version of Windows requires _PS3 to be implemented

Method(_PS3, 0) { return(STA) }

// TODO: SPIs are not available to the guest on AARCH64, which is what
// PcdVmbusVector is currently defined as. Supposedly it should use a PPI,
// but those are strange because they're reserved for hypervisor devices.
//
// Windows doesn't boot when VmBus is given an SPI, since it's unable to
// allocate any since none exist in guests. Thus, leave it out on AARCH64
// for now.
//
// Linux may need this field if it's not hardcoded, unsure.
//
// Additionally, no Interrupt-Signaled event devices currently work either,
// due to SPIs not being available to guests.
Name(_CRS,
Name(_DDN, "VMBUS")
Name(_HID, "MSFT1000")
Name(_CID, "VMBus")
Name(_UID, 0)
Method(_DIS, 0) { And(STA, 0xD, STA) }
Method(_PS0, 0) { Or(STA, 0xF, STA) }
Method(_STA, 0)
{
return(STA)
}

// Include an interrupt resource so that Linux VMs can get IDT
// entries.
//
// N.B. All Windows VMs that support UEFI also support
// getting IDT entries via other mechanisms, so this is not
// necessary for Windows.
// Older versions of this DSDT implemented _PS3 improperly, as:
// Name(_PS3, 0)
// This is intentionally a do-nothing method in case any version of Windows requires _PS3 to be implemented

ResourceTemplate()
{
Method(_PS3, 0) { return(STA) }

// TODO: SPIs are not available to the guest on AARCH64, which is what
// PcdVmbusVector is currently defined as. Supposedly it should use a PPI,
// but those are strange because they're reserved for hypervisor devices.
//
// Windows doesn't boot when VmBus is given an SPI, since it's unable to
// allocate any since none exist in guests. Thus, leave it out on AARCH64
// for now.
//
// Linux may need this field if it's not hardcoded, unsure.
//
// Additionally, no Interrupt-Signaled event devices currently work either,
// due to SPIs not being available to guests.
Name(_CRS,

// Include an interrupt resource so that Linux VMs can get IDT
// entries.
//
// N.B. All Windows VMs that support UEFI also support
// getting IDT entries via other mechanisms, so this is not
// necessary for Windows.

ResourceTemplate()
{

#if defined(_DSDT_INTEL_)

// Older Linux kernels like RHEL/CentOS don't seem to be able to
// parse the new Extended Interrupt Descriptor resource type (see ACPI Section 6.4.3.6),
// so we instead use the old legacy IRQ description which
// becomes the short form of Interrupt Descriptor (ACPI Section 5.4.2.1)
// which only supports legacy PIC devices to describe up to 15
// interrupts. VMBUS is interrupt 5 on X64, so this is okay.
IRQ(Edge,ActiveHigh,Exclusive)
{FixedPcdGet8(PcdVmbusVector)}
// Older Linux kernels like RHEL/CentOS don't seem to be able to
// parse the new Extended Interrupt Descriptor resource type (see ACPI Section 6.4.3.6),
// so we instead use the old legacy IRQ description which
// becomes the short form of Interrupt Descriptor (ACPI Section 5.4.2.1)
// which only supports legacy PIC devices to describe up to 15
// interrupts. VMBUS is interrupt 5 on X64, so this is okay.
IRQ(Edge,ActiveHigh,Exclusive)
{FixedPcdGet8(PcdVmbusVector)}

#else
// On AArch64, we select a PPI (16) because Linux expects it to
// be available to all CPUs.
Interrupt(ResourceConsumer, Edge, ActiveHigh, Exclusive)
{FixedPcdGet8(PcdVmbusVector)}
// On AArch64, we select a PPI (16) because Linux expects it to
// be available to all CPUs.
Interrupt(ResourceConsumer, Edge, ActiveHigh, Exclusive)
{FixedPcdGet8(PcdVmbusVector)}

#endif
}
)
}
)
}
}

// TPM ====================================================================
Expand Down
4 changes: 3 additions & 1 deletion MsvmPkg/Include/BiosInterface.h
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Expand Up @@ -789,7 +789,9 @@ typedef struct _UEFI_CONFIG_FLAGS
UINT64 Dhcp6DuidTypeLlt : 1;
UINT64 CxlMemoryEnabled : 1;
UINT64 MtrrsInitializedAtLoad : 1;
UINT64 Reserved:35;
UINT64 HvSintEnabled : 1; // Reserved; used by other codebase.
UINT64 VmbusDisabled : 1;
UINT64 Reserved:33;
} Flags;
} UEFI_CONFIG_FLAGS;

Expand Down
4 changes: 4 additions & 0 deletions MsvmPkg/Library/DeviceBootManagerLib/DeviceBootManagerLib.c
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Expand Up @@ -425,6 +425,10 @@ DeviceBootManagerBeforeConsole (
*DevicePath = NULL;
*PlatformConsoles = NULL;

if (!PcdGetBool(PcdVmbusEnabled)) {
goto Exit;
}

Status = gBS->LocateHandleBuffer (
ByProtocol,
&gEfiVmbusProtocolGuid,
Expand Down
1 change: 1 addition & 0 deletions MsvmPkg/Library/DeviceBootManagerLib/DeviceBootManagerLib.inf
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Expand Up @@ -69,6 +69,7 @@ CONSTRUCTOR = DeviceBootManagerConstructor
gMsvmPkgTokenSpaceGuid.PcdIsVmbfsBoot
gMsvmPkgTokenSpaceGuid.PcdLogoFile
gMsvmPkgTokenSpaceGuid.PcdPxeIpV6
gMsvmPkgTokenSpaceGuid.PcdVmbusEnabled
gMsvmPkgTokenSpaceGuid.PcdVpciBootEnabled

[Depex]
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1 change: 1 addition & 0 deletions MsvmPkg/MsvmPkg.dec
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Expand Up @@ -298,6 +298,7 @@
gMsvmPkgTokenSpaceGuid.PcdHostEmulatorsWhenHardwareIsolated|FALSE|BOOLEAN|0x6064
gMsvmPkgTokenSpaceGuid.PcdTpmLocalityRegsEnabled|FALSE|BOOLEAN|0x6065
gMsvmPkgTokenSpaceGuid.PcdMtrrsInitializedAtLoad|FALSE|BOOLEAN|0x6067
gMsvmPkgTokenSpaceGuid.PcdVmbusEnabled|TRUE|BOOLEAN|0x6068

# UEFI_CONFIG_PROCESSOR_INFORMATION
gMsvmPkgTokenSpaceGuid.PcdProcessorCount|0x0|UINT32|0x6032
Expand Down
1 change: 1 addition & 0 deletions MsvmPkg/MsvmPkgAARCH64.dsc
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Expand Up @@ -697,6 +697,7 @@
gMsvmPkgTokenSpaceGuid.PcdWatchdogEnabled|FALSE
gMsvmPkgTokenSpaceGuid.PcdHostEmulatorsWhenHardwareIsolated|FALSE
gMsvmPkgTokenSpaceGuid.PcdTpmLocalityRegsEnabled|FALSE
gMsvmPkgTokenSpaceGuid.PcdVmbusEnabled|TRUE

# UEFI_CONFIG_PROCESSOR_INFORMATION
gMsvmPkgTokenSpaceGuid.PcdProcessorCount|0x0
Expand Down
1 change: 1 addition & 0 deletions MsvmPkg/MsvmPkgX64.dsc
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Expand Up @@ -715,6 +715,7 @@
gMsvmPkgTokenSpaceGuid.PcdWatchdogEnabled|FALSE
gMsvmPkgTokenSpaceGuid.PcdHostEmulatorsWhenHardwareIsolated|FALSE
gMsvmPkgTokenSpaceGuid.PcdTpmLocalityRegsEnabled|FALSE
gMsvmPkgTokenSpaceGuid.PcdVmbusEnabled|TRUE

# UEFI_CONFIG_PROCESSOR_INFORMATION
gMsvmPkgTokenSpaceGuid.PcdProcessorCount|0x0
Expand Down
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