Re: [edk2-devel] [edk2][RFC] OvmfPkg/AcpiPlatformDxe: patch FADT PSCI bits if FDT advertises it

["Laszlo Ersek" <lersek@redhat.com>]

On 9/7/23 16:27, Ard Biesheuvel wrote:
> On Mon, 16 Jan 2023 at 12:39, Evgeny Iakovlev
> <eiakovlev@linux.microsoft.com> wrote:
>>
>> EL3 firmware may implement PSCI interface on aarch64 platforms,
>> including qemu-tcg-aarch64. However, EL3 firmware does not usually own
>> pulling and deploying ACPI tables from qemu fw_cfg. Thus the only way
>> EL3 can advertise PSCI on qemu is in FDT. One such EL3 fw is ARM trusted
>> firmware. Qemu itself also won't advertise PSCI in either FDT or ACPI if
>> EL3 firmware is present.
>>
>> PSCI can be advertised in both FDT and ACPI, and Hyper-V/NT kernel
>> expect to see all information published in ACPI. To better support
>> running Hyper-V/NT on qemu-tcg-aarch64 with EDK2 as UEFI implementation
>> and ARM trusted firmware as EL3 PSCI implementation we can patch in PSCI
>> bits in ACPI FADT when pulling tables from fw_cfg if PSCI node is
>> advertised in FDT. EDK2 owns ACPI table publishing and is also aware of
>> FDT on arm, so it is ideally poised to handle this.
>>
>> This change illustrates how it could potentially be done. I am looking
>> for comments on overall validity of the idea to patch FADT and whether
>> or not this particular approach of handling it in AcpiPlatformDxe is the
>> way to do it or maybe it is better to handle it via
>> gQemuAcpiTableNotifyProtocolGuid somehow.
>>
>> Signed-off-by: Evgeny Iakovlev <eiakovlev@linux.microsoft.com>
> 
> Thanks for the patch, and apologies for the lack of response.
> 
> First of all, I suspect this patch breaks non-ARM users of this
> driver, so the patch is problematic as is. (It makes
> gFdtClientProtocolGuid mandatory, right?)
> 
> Then, I'd like to hear from other folks on cc what they think about
> this. Perhaps it is simply a matter of tweaking QEMU so it exposes the
> correct PSCI setting in the FADT when it emulates secure world.
> Patching it like this feels like a last resort to me, rather than a
> well designed interface.

Thanks for the CC; both of your concerns are valid.

The FDT client proto GUID has no reason to exist in (e.g.) an X64 OVMF
build.

Second, and more importantly, this is a total layering violation for
AcpiPlatformDxe. QEMU is the single source of truth for AcpiPlatformDxe,
and AcpiPlatformDxe must remain as blind as possible to the actual ACPI
content.

In the situation described by the commit message, the ACPI content
exposed by QEMU is simply invalid. That's what should be fixed in QEMU
(and not papered over in edk2). Something somewhere is responsible for
setting the property value in question to "hvc"; that something
precisely is responsible (directly or indirectly) for making QEMU expose
the proper FADT.

I've now grepped the QEMU source tree for '"hvc"'; the relevant hit
seems to be in "hw/arm/boot.c", function fdt_add_psci_node(), under case
label QEMU_PSCI_CONDUIT_HVC. So, whatever sets psci-conduit to
QEMU_PSCI_CONDUIT_HVC should also make sure the FADT matches it.

Taking one step back, in "hw/arm/virt.c" we have:

    if (vms->secure && firmware_loaded) {
        vms->psci_conduit = QEMU_PSCI_CONDUIT_DISABLED;
    } else if (vms->virt) {
        vms->psci_conduit = QEMU_PSCI_CONDUIT_SMC;
    } else {
        vms->psci_conduit = QEMU_PSCI_CONDUIT_HVC;
    }

So I figure the ACPI generator should be steered off the same information.

BTW... I see the following in "hw/arm/virt-acpi-build.c", function
build_fadt_rev6():

    case QEMU_PSCI_CONDUIT_HVC:
        fadt.arm_boot_arch = ACPI_FADT_ARM_PSCI_COMPLIANT |
                             ACPI_FADT_ARM_PSCI_USE_HVC;
        break;

That dates back minimally as far as commit 79e993a0a804
("hw/arm/virt-acpi-build: use SMC if booting in EL2", 2017-01-20).

So why is it not taking effect? Patching edk2 should not be necessary at
all, QEMU should already be doing the right thing.

The commit message states, "Qemu itself also won't advertise PSCI in
[...] ACPI if EL3 firmware is present"; if that's correct (I can't
tell), then it may be the problem.

Thanks
Laszlo

> 
> 
>> ---
>> Resending the message because i wasn't subscribed to the rfc group the
>> last time, sorry.
>> ---
>>  OvmfPkg/AcpiPlatformDxe/AcpiPlatformDxe.inf |   4 +-
>>  OvmfPkg/AcpiPlatformDxe/QemuFwCfgAcpi.c     | 108 ++++++++++++++++++++
>>  2 files changed, 111 insertions(+), 1 deletion(-)
>>
>> diff --git a/OvmfPkg/AcpiPlatformDxe/AcpiPlatformDxe.inf b/OvmfPkg/AcpiPlatformDxe/AcpiPlatformDxe.inf
>> index 8939dde425..a011a43743 100644
>> --- a/OvmfPkg/AcpiPlatformDxe/AcpiPlatformDxe.inf
>> +++ b/OvmfPkg/AcpiPlatformDxe/AcpiPlatformDxe.inf
>> @@ -30,6 +30,7 @@
>>    QemuFwCfgAcpi.c
>>
>>  [Packages]
>> +  EmbeddedPkg/EmbeddedPkg.dec
>>    MdeModulePkg/MdeModulePkg.dec
>>    MdePkg/MdePkg.dec
>>    OvmfPkg/OvmfPkg.dec
>> @@ -50,6 +51,7 @@
>>  [Protocols]
>>    gEfiAcpiTableProtocolGuid                     # PROTOCOL ALWAYS_CONSUMED
>>    gEfiPciIoProtocolGuid                         # PROTOCOL SOMETIMES_CONSUMED
>> +  gFdtClientProtocolGuid                        # PROTOCOL SOMETIMES_CONSUMED
>>    gQemuAcpiTableNotifyProtocolGuid              # PROTOCOL PRODUCES
>>
>>  [Guids]
>> @@ -64,4 +66,4 @@
>>    gEfiMdePkgTokenSpaceGuid.PcdConfidentialComputingGuestAttr
>>
>>  [Depex]
>> -  gEfiAcpiTableProtocolGuid
>> +  gEfiAcpiTableProtocolGuid AND gFdtClientProtocolGuid
>> diff --git a/OvmfPkg/AcpiPlatformDxe/QemuFwCfgAcpi.c b/OvmfPkg/AcpiPlatformDxe/QemuFwCfgAcpi.c
>> index c8dee17c13..31d8665d2d 100644
>> --- a/OvmfPkg/AcpiPlatformDxe/QemuFwCfgAcpi.c
>> +++ b/OvmfPkg/AcpiPlatformDxe/QemuFwCfgAcpi.c
>> @@ -9,6 +9,7 @@
>>  **/
>>
>>  #include <IndustryStandard/Acpi.h>            // EFI_ACPI_DESCRIPTION_HEADER
>> +#include <IndustryStandard/Acpi51.h>          // EFI_ACPI_5_1_FIXED_ACPI_DESCRIPTION_TABLE
>>  #include <IndustryStandard/QemuLoader.h>      // QEMU_LOADER_FNAME_SIZE
>>  #include <Library/BaseLib.h>                  // AsciiStrCmp()
>>  #include <Library/BaseMemoryLib.h>            // CopyMem()
>> @@ -20,6 +21,7 @@
>>  #include <Library/UefiBootServicesTableLib.h> // gBS
>>
>>  #include <Protocol/QemuAcpiTableNotify.h>
>> +#include <Protocol/FdtClient.h>
>>  #include "AcpiPlatform.h"
>>  EFI_HANDLE                       mQemuAcpiHandle = NULL;
>>  QEMU_ACPI_TABLE_NOTIFY_PROTOCOL  mAcpiNotifyProtocol;
>> @@ -815,6 +817,92 @@ UndoCmdWritePointer (
>>      ));
>>  }
>>
>> +/**
>> +  Locate a PSCI node in DTB published by EL3 firmware that implemented it
>> +  and use information in it to patch ACPI FADT PSCI bits.
>> +
>> +  The reason for it is that EL3 PSCI implementation, which is not EDK2,
>> +  doesn't own ACPI tables and cannot advertise it there itself, it is using DTB instead.
>> +
>> +  Qemu also won't advertise PSCI if EL3 firmware is present.
>> +  A real example of that is running ARM trusted firmware in EL3 with PSCI enabled.
>> +
>> +  @param[in] PonterValue    FADT base address
>> +
>> +  @param[in] TableSize      Size of table in bytes
>> +
>> +  @return                   EFI_SUCCESS if FAST was patched or if patching was not needed,
>> +                            error status returned by FDT client protocol otherwise.
>> +**/
>> +STATIC
>> +EFI_STATUS
>> +EFIAPI
>> +PatchFadtPsciBits (
>> +  IN UINT64     PointerValue,
>> +  IN UINTN      TableSize
>> +  )
>> +{
>> +  EFI_STATUS                                    Status;
>> +  FDT_CLIENT_PROTOCOL                           *FdtClient;
>> +  CONST VOID                                    *Prop;
>> +  EFI_ACPI_5_1_FIXED_ACPI_DESCRIPTION_TABLE     *Fadt;
>> +  UINT8                                         MajorMinorRev;
>> +
>> +  Status = gBS->LocateProtocol (
>> +                  &gFdtClientProtocolGuid,
>> +                  NULL,
>> +                  (VOID **)&FdtClient
>> +                  );
>> +  if (Status == EFI_NOT_FOUND) {
>> +    goto NoPatchingNeeded;
>> +  } else if (EFI_ERROR (Status)) {
>> +    return Status;
>> +  }
>> +
>> +  Status = FdtClient->FindCompatibleNodeProperty (
>> +                        FdtClient,
>> +                        "arm,psci-0.2",
>> +                        "method",
>> +                        &Prop,
>> +                        NULL
>> +                        );
>> +  if (Status == EFI_NOT_FOUND) {
>> +    goto NoPatchingNeeded;
>> +  } else if (EFI_ERROR (Status)) {
>> +    return Status;
>> +  }
>> +
>> +  //
>> +  // Make sure FADT is large enough for 5.1
>> +  //
>> +  if (TableSize < sizeof (*Fadt)) {
>> +    goto NoPatchingNeeded;
>> +  }
>> +
>> +  Fadt = (EFI_ACPI_5_1_FIXED_ACPI_DESCRIPTION_TABLE *)(UINTN)PointerValue;
>> +
>> +  //
>> +  // Check that FADT revision is at least 5.1 now that it's safe to read fields
>> +  //
>> +  MajorMinorRev = (Fadt->Header.Revision << 4) | (Fadt->MinorVersion & 0x0F);
>> +  if (MajorMinorRev < 0x51) {
>> +    goto NoPatchingNeeded;
>> +  }
>> +
>> +  //
>> +  // Patch FADT PSCI bits
>> +  //
>> +  Fadt->ArmBootArch = EFI_ACPI_5_1_ARM_PSCI_COMPLIANT;
>> +  if (AsciiStrnCmp (Prop, "hvc", 3) == 0) {
>> +    Fadt->ArmBootArch |= EFI_ACPI_5_1_ARM_PSCI_USE_HVC;
>> +  }
>> +
>> +  return EFI_SUCCESS;
>> +
>> +NoPatchingNeeded:
>> +  return EFI_SUCCESS;
>> +}
>> +
>>  //
>>  // We'll be saving the keys of installed tables so that we can roll them back
>>  // in case of failure. 128 tables should be enough for anyone (TM).
>> @@ -901,6 +989,7 @@ Process2ndPassCmdAddPointer (
>>    UINT64                                              PointerValue;
>>    UINTN                                               Blob2Remaining;
>>    UINTN                                               TableSize;
>> +  UINT32                                              Signature;
>>    CONST EFI_ACPI_1_0_FIRMWARE_ACPI_CONTROL_STRUCTURE  *Facs;
>>    CONST EFI_ACPI_DESCRIPTION_HEADER                   *Header;
>>    EFI_STATUS                                          Status;
>> @@ -960,6 +1049,7 @@ Process2ndPassCmdAddPointer (
>>      ));
>>
>>    TableSize = 0;
>> +  Signature = 0;
>>
>>    //
>>    // To make our job simple, the FACS has a custom header. Sigh.
>> @@ -979,6 +1069,7 @@ Process2ndPassCmdAddPointer (
>>          Facs->Length
>>          ));
>>        TableSize = Facs->Length;
>> +      Signature = Facs->Signature;
>>      }
>>    }
>>
>> @@ -1004,6 +1095,7 @@ Process2ndPassCmdAddPointer (
>>          Header->Length
>>          ));
>>        TableSize = Header->Length;
>> +      Signature = Header->Signature;
>>
>>        //
>>        // Skip RSDT and XSDT because those are handled by
>> @@ -1035,6 +1127,22 @@ Process2ndPassCmdAddPointer (
>>      goto RollbackSeenPointer;
>>    }
>>
>> +  //
>> +  // For FADT also patch PSCI flag if DTB exposes it.
>> +  //
>> +  if (Signature == EFI_ACPI_1_0_FIXED_ACPI_DESCRIPTION_TABLE_SIGNATURE) {
>> +    Status = PatchFadtPsciBits(PointerValue, TableSize);
>> +    if (EFI_ERROR (Status)) {
>> +      DEBUG ((
>> +        DEBUG_ERROR,
>> +        "%a: PatchFadtPsciBits(): %r\n",
>> +        __FUNCTION__,
>> +        Status
>> +        ));
>> +      goto RollbackSeenPointer;
>> +    }
>> +  }
>> +
>>    Status = AcpiProtocol->InstallAcpiTable (
>>                             AcpiProtocol,
>>                             (VOID *)(UINTN)PointerValue,
>> --
>> 2.38.1.vfs.0.0
>>
> 



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