Re: [PATCH v2 13/17] OvmfPkg/PvScsiDxe: Setup requests and completions rings

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

On 03/25/20 17:10, Liran Alon wrote:
> These rings are shared memory buffers between host and device in which
> a cyclic buffer is managed to send request descriptors from host to
> device and receive completion descriptors from device to host.
>
> Note that because device may be constrained by IOMMU or guest may be run
> under AMD SEV, we make sure to map these rings to device by using
> PciIo->Map().
>
> Ref: https://bugzilla.tianocore.org/show_bug.cgi?id=2567
> Signed-off-by: Liran Alon <liran.alon@oracle.com>
> ---
>  OvmfPkg/PvScsiDxe/PvScsi.c | 269 +++++++++++++++++++++++++++++++++++++
>  OvmfPkg/PvScsiDxe/PvScsi.h |  17 +++
>  2 files changed, 286 insertions(+)
>
> diff --git a/OvmfPkg/PvScsiDxe/PvScsi.c b/OvmfPkg/PvScsiDxe/PvScsi.c
> index 831a78cc18c7..59863f83c60c 100644
> --- a/OvmfPkg/PvScsiDxe/PvScsi.c
> +++ b/OvmfPkg/PvScsiDxe/PvScsi.c
> @@ -16,6 +16,7 @@
>  #include <Library/UefiBootServicesTableLib.h>
>  #include <Library/UefiLib.h>
>  #include <Protocol/PciIo.h>
> +#include <Protocol/PciRootBridgeIo.h>
>  #include <Uefi/UefiSpec.h>
>
>  #include "PvScsi.h"
> @@ -413,6 +414,264 @@ PvScsiRestorePciAttributes (
>                  );
>  }
>
> +STATIC
> +EFI_STATUS
> +PvScsiAllocatePages (
> +  IN PVSCSI_DEV     *Dev,
> +  IN UINTN          Pages,
> +  IN OUT VOID       **HostAddress
> +  )
> +{
> +  return Dev->PciIo->AllocateBuffer (
> +                       Dev->PciIo,
> +                       AllocateAnyPages,
> +                       EfiBootServicesData,
> +                       Pages,
> +                       HostAddress,
> +                       EFI_PCI_ATTRIBUTE_MEMORY_CACHED
> +                       );
> +}
> +
> +STATIC
> +VOID
> +PvScsiFreePages (
> +  IN PVSCSI_DEV     *Dev,
> +  IN UINTN          Pages,
> +  IN VOID           *HostAddress
> +  )
> +{
> +  Dev->PciIo->FreeBuffer (
> +                Dev->PciIo,
> +                Pages,
> +                HostAddress
> +                );
> +}
> +
> +STATIC
> +EFI_STATUS
> +PvScsiMapBuffer (
> +  IN PVSCSI_DEV                     *Dev,
> +  IN EFI_PCI_IO_PROTOCOL_OPERATION  PciIoOperation,
> +  IN VOID                           *HostAddress,
> +  IN UINTN                          NumberOfBytes,
> +  OUT PVSCSI_DMA_DESC               *DmaDesc
> +  )
> +{
> +  EFI_STATUS Status;
> +  UINTN      BytesMapped;
> +
> +  BytesMapped = NumberOfBytes;
> +  Status = Dev->PciIo->Map (
> +                         Dev->PciIo,
> +                         PciIoOperation,
> +                         HostAddress,
> +                         &BytesMapped,
> +                         &DmaDesc->DeviceAddress,
> +                         &DmaDesc->Mapping
> +                         );
> +  if (EFI_ERROR (Status)) {
> +    return Status;
> +  }
> +
> +  if (BytesMapped != NumberOfBytes) {
> +    Status = EFI_OUT_OF_RESOURCES;
> +    goto Unmap;
> +  }
> +
> +  return EFI_SUCCESS;
> +
> +Unmap:
> +  Dev->PciIo->Unmap (Dev->PciIo, DmaDesc->Mapping);
> +
> +  return Status;
> +}
> +
> +STATIC
> +VOID
> +PvScsiUnmapBuffer (
> +  IN PVSCSI_DEV                 *Dev,
> +  IN OUT PVSCSI_DMA_DESC        *DmaDesc)
> +{
> +  Dev->PciIo->Unmap (Dev->PciIo, DmaDesc->Mapping);
> +}
> +
> +STATIC
> +EFI_STATUS
> +PvScsiAllocateSharedPages (
> +  IN PVSCSI_DEV                     *Dev,
> +  IN UINTN                          Pages,
> +  IN EFI_PCI_IO_PROTOCOL_OPERATION  PciIoOperation,
> +  OUT VOID                          **HostAddress,
> +  OUT PVSCSI_DMA_DESC               *DmaDesc
> +  )
> +{
> +  EFI_STATUS Status;
> +
> +  Status = PvScsiAllocatePages (Dev, Pages, HostAddress);
> +  if (EFI_ERROR (Status)) {
> +    return Status;
> +  }
> +
> +  Status = PvScsiMapBuffer (
> +             Dev,
> +             PciIoOperation,
> +             *HostAddress,
> +             EFI_PAGES_TO_SIZE (Pages),
> +             DmaDesc
> +             );
> +  if (EFI_ERROR (Status)) {
> +    goto FreePages;
> +  }
> +
> +  return EFI_SUCCESS;
> +
> +FreePages:
> +  PvScsiFreePages (Dev, Pages, *HostAddress);
> +
> +  return Status;
> +}
> +
> +STATIC
> +VOID
> +PvScsiFreeSharedPages (
> +  IN PVSCSI_DEV                     *Dev,
> +  IN UINTN                          Pages,
> +  IN OUT VOID                       *HostAddress,
> +  IN OUT PVSCSI_DMA_DESC            *DmaDesc
> +  )
> +{
> +  PvScsiUnmapBuffer (Dev, DmaDesc);
> +  PvScsiFreePages (Dev, Pages, HostAddress);
> +}

(1) From all of the above functions, please keep only two:
PvScsiAllocateSharedPages() and PvScsiFreeSharedPages(). The rest of the
helper functions should be flattened into them.

This is not a "frivolous" request -- it will make more sense once you
read my next request.

(2) Please eliminate the "PciIoOperation" parameter from the
PvScsiAllocateSharedPages() prototype, and open-code
"EfiPciIoOperationBusMasterCommonBuffer" in its place, in the
(flattened) implementation of the function.


Rationale: the buffer should be allocated separately with the
PciIo->AllocateBuffer() API *if and only if* a common buffer operation
is being set up. In other cases (one-shot bus master read, one-shot bus
master write), *only* the Map() operation should be used, and then Map()
and Unmap() will handle the bounce-buffering internally.

The functions above are misleading because they suggest they handle all
three bus master operations -- but for the one-shot BM read and write
operations, the PvScsiAllocateSharedPages() / PvScsiFreeSharedPages()
implementations are not correct.

Now, given that the call sites only set up common buffer operations, the
ultimately exercised logic is OK. And therefore the solution is not to
generalize the implementation uselessly (to BM read and BM write
operations too), but to tighten the interfaces such that they precisely
reflect the actual intended use case.

Hence, please open-code the common buffer operation internally to
PvScsiAllocateSharedPages(), and also stop exposing the separate
allocation / freeing / mapping / unmapping interfaces. The call sites
need nothing else than (a) "give me a completely mapped range for common
buffer operation" and (b) "release that".

Here's the (untested, not even compiled) implementation I propose:

> STATIC
> EFI_STATUS
> PvScsiAllocateSharedPages (
>   IN PVSCSI_DEV       *Dev,
>   IN UINTN            Pages,
>   OUT VOID            **HostAddress,
>   OUT PVSCSI_DMA_DESC *DmaDesc
>   )
> {
>   EFI_STATUS Status;
>   UINTN      NumberOfBytes;
>
>   Status = Dev->PciIo->AllocateBuffer (
>                          Dev->PciIo,
>                          AllocateAnyPages,
>                          EfiBootServicesData,
>                          Pages,
>                          HostAddress,
>                          EFI_PCI_ATTRIBUTE_MEMORY_CACHED
>                          );
>   if (EFI_ERROR (Status)) {
>     return Status;
>   }
>
>   NumberOfBytes = EFI_PAGES_TO_SIZE (Pages);
>   Status = Dev->PciIo->Map (
>                          Dev->PciIo,
>                          EfiPciIoOperationBusMasterCommonBuffer,
>                          *HostAddress,
>                          &NumberOfBytes,
>                          &DmaDesc->DeviceAddress,
>                          &DmaDesc->Mapping
>                          );
>   if (EFI_ERROR (Status)) {
>     goto FreeBuffer;
>   }
>
>   if (NumberOfBytes != EFI_PAGES_TO_SIZE (Pages)) {
>     Status = EFI_OUT_OF_RESOURCES;
>     goto Unmap;
>   }
>
>   return EFI_SUCCESS;
>
> Unmap:
>   Dev->PciIo->Unmap (Dev->PciIo, DmaDesc->Mapping);
>
> FreeBuffer:
>   Dev->PciIo->FreeBuffer (Dev->PciIo, Pages, *HostAddress);
>
>   return Status;
> }
>
> STATIC
> VOID
> PvScsiFreeSharedPages (
>   IN PVSCSI_DEV      *Dev,
>   IN UINTN           Pages,
>   IN VOID            *HostAddress,
>   IN PVSCSI_DMA_DESC *DmaDesc
>   )
> {
>   Dev->PciIo->Unmap (Dev->PciIo, DmaDesc->Mapping);
>   Dev->PciIo->FreeBuffer (Dev->PciIo, Pages, HostAddress);
> }

Back to your patch:

On 03/25/20 17:10, Liran Alon wrote:
> +
> +STATIC
> +EFI_STATUS
> +PvScsiInitRings (
> +  IN OUT PVSCSI_DEV *Dev
> +  )
> +{
> +  EFI_STATUS                  Status;
> +  PVSCSI_CMD_DESC_SETUP_RINGS Cmd;
> +
> +  Status = PvScsiAllocateSharedPages (
> +             Dev,
> +             1,
> +             EfiPciIoOperationBusMasterCommonBuffer,
> +             (VOID **)&Dev->RingDesc.RingState,
> +             &Dev->RingDesc.RingStateDmaDesc
> +             );
> +  if (EFI_ERROR (Status)) {
> +    return Status;
> +  }
> +  ZeroMem (Dev->RingDesc.RingState, EFI_PAGE_SIZE);
> +
> +  Status = PvScsiAllocateSharedPages (
> +             Dev,
> +             1,
> +             EfiPciIoOperationBusMasterCommonBuffer,
> +             (VOID **)&Dev->RingDesc.RingReqs,
> +             &Dev->RingDesc.RingReqsDmaDesc
> +             );
> +  if (EFI_ERROR (Status)) {
> +    goto FreeRingState;
> +  }
> +  ZeroMem (Dev->RingDesc.RingReqs, EFI_PAGE_SIZE);
> +
> +  Status = PvScsiAllocateSharedPages (
> +             Dev,
> +             1,
> +             EfiPciIoOperationBusMasterCommonBuffer,
> +             (VOID **)&Dev->RingDesc.RingCmps,
> +             &Dev->RingDesc.RingCmpsDmaDesc
> +             );
> +  if (EFI_ERROR (Status)) {
> +    goto FreeRingReqs;
> +  }
> +  ZeroMem (Dev->RingDesc.RingCmps, EFI_PAGE_SIZE);
> +
> +  ZeroMem (&Cmd, sizeof (Cmd));
> +  Cmd.ReqRingNumPages = 1;
> +  Cmd.CmpRingNumPages = 1;
> +  Cmd.RingsStatePPN = RShiftU64 (
> +                        (UINT64)Dev->RingDesc.RingStateDmaDesc.DeviceAddress,
> +                        EFI_PAGE_SHIFT
> +                        );
> +  Cmd.ReqRingPPNs[0] = RShiftU64 (
> +                         (UINT64)Dev->RingDesc.RingReqsDmaDesc.DeviceAddress,
> +                         EFI_PAGE_SHIFT
> +                         );
> +  Cmd.CmpRingPPNs[0] = RShiftU64 (
> +                         (UINT64)Dev->RingDesc.RingCmpsDmaDesc.DeviceAddress,
> +                         EFI_PAGE_SHIFT
> +                         );

(3) Please drop the explicit UINT64 casts -- for brevity --,
EFI_PHYSICAL_ADDRESS is just a different name (a typedef) for UINT64, by
spec. (See in the EFI_BOOT_SERVICES.AllocatePages() chapter in the UEFI
spec.)

(4) Please #include <Library/BaseLib.h> in the C file, and also list
BaseLib under [LibraryClasses] in the INF file. RShiftU64() comes from
there.

> +
> +  Status = PvScsiWriteCmdDesc (
> +             Dev,
> +             PvScsiCmdSetupRings,
> +             (UINT32 *)&Cmd,

(5) So I guess this is where the "union trick" will come, in v3.

> +             sizeof (Cmd) / sizeof (UINT32)

(6) Can you please try inserting, before the PvScsiWriteCmdDesc() call:

  STATIC_ASSERT (sizeof Cmd % sizeof (UINT32) == 0, "invalid Cmd size");

> +             );
> +  if (EFI_ERROR (Status)) {
> +    goto FreeRingCmps;
> +  }
> +
> +  return EFI_SUCCESS;
> +
> +FreeRingCmps:
> +  PvScsiFreeSharedPages (
> +    Dev,
> +    1,
> +    Dev->RingDesc.RingCmps,
> +    &Dev->RingDesc.RingCmpsDmaDesc
> +    );
> +
> +FreeRingReqs:
> +  PvScsiFreeSharedPages (
> +    Dev,
> +    1,
> +    Dev->RingDesc.RingReqs,
> +    &Dev->RingDesc.RingReqsDmaDesc
> +    );
> +
> +FreeRingState:
> +  PvScsiFreeSharedPages (
> +    Dev,
> +    1,
> +    Dev->RingDesc.RingState,
> +    &Dev->RingDesc.RingStateDmaDesc
> +    );
> +
> +  return Status;
> +}
> +
> +STATIC
> +VOID
> +PvScsiFreeRings (
> +  IN OUT PVSCSI_DEV *Dev
> +  )
> +{
> +  PvScsiFreeSharedPages (
> +    Dev,
> +    1,
> +    Dev->RingDesc.RingCmps,
> +    &Dev->RingDesc.RingCmpsDmaDesc
> +    );
> +
> +  PvScsiFreeSharedPages (
> +    Dev,
> +    1,
> +    Dev->RingDesc.RingReqs,
> +    &Dev->RingDesc.RingReqsDmaDesc
> +    );
> +
> +  PvScsiFreeSharedPages (
> +    Dev,
> +    1,
> +    Dev->RingDesc.RingState,
> +    &Dev->RingDesc.RingStateDmaDesc
> +    );
> +}
> +

(7) This function is almost correct.

Note that your last *such* action in PvScsiInitRings() that impacts any
resource life cycle is the *exposure* of the rings to the device model
(the hypervisor).

Therefore, after PvScsiInitRings() succeeds, then on any subsequently
occurring error path, you first need to make the device model forget
about the rings, before you release the rings. A hypervisor-side
reference to guest memory is just another resource you "allocate", so
you need to drop it too, in reverse order of construction.

In brief, please add the following to the top of the PvScsiFreeRings()
function:

  PvScsiWriteCmdDesc (Dev, PvScsiCmdAdapterReset, NULL, 0);

(Consider, for example, what would happen *otherwise*, if the DmaBuf
allocation failed -- in the next patch -- in the PvScsiInit() function.

There, you jump to "FreeRings" correctly, and release the rings with
PvScsiFreeRings() -- but the hypervisor still remembers them!)

>  STATIC
>  EFI_STATUS
>  PvScsiInit (
> @@ -443,6 +702,14 @@ PvScsiInit (
>      goto RestorePciAttributes;
>    }
>
> +  //
> +  // Init PVSCSI rings
> +  //
> +  Status = PvScsiInitRings (Dev);
> +  if (EFI_ERROR (Status)) {
> +    goto RestorePciAttributes;
> +  }
> +
>    //
>    // Populate the exported interface's attributes
>    //
> @@ -486,6 +753,8 @@ PvScsiUninit (
>    IN OUT PVSCSI_DEV *Dev
>    )
>  {
> +  PvScsiFreeRings (Dev);
> +
>    PvScsiRestorePciAttributes (Dev);
>  }
>
> diff --git a/OvmfPkg/PvScsiDxe/PvScsi.h b/OvmfPkg/PvScsiDxe/PvScsi.h
> index 5f611dbbc98c..6d23b6e1eccf 100644
> --- a/OvmfPkg/PvScsiDxe/PvScsi.h
> +++ b/OvmfPkg/PvScsiDxe/PvScsi.h
> @@ -15,12 +15,29 @@
>  #include <Library/DebugLib.h>
>  #include <Protocol/ScsiPassThruExt.h>
>
> +typedef struct {
> +  EFI_PHYSICAL_ADDRESS DeviceAddress;
> +  VOID                 *Mapping;
> +} PVSCSI_DMA_DESC;
> +
> +typedef struct {
> +  PVSCSI_RINGS_STATE   *RingState;
> +  PVSCSI_DMA_DESC      RingStateDmaDesc;
> +
> +  PVSCSI_RING_REQ_DESC *RingReqs;
> +  PVSCSI_DMA_DESC      RingReqsDmaDesc;
> +
> +  PVSCSI_RING_CMP_DESC *RingCmps;
> +  PVSCSI_DMA_DESC      RingCmpsDmaDesc;
> +} PVSCSI_RING_DESC;
> +
>  #define PVSCSI_SIG SIGNATURE_32 ('P', 'S', 'C', 'S')
>
>  typedef struct {
>    UINT32                          Signature;
>    EFI_PCI_IO_PROTOCOL             *PciIo;
>    UINT64                          OriginalPciAttributes;
> +  PVSCSI_RING_DESC                RingDesc;
>    UINT8                           MaxTarget;
>    UINT8                           MaxLun;
>    EFI_EXT_SCSI_PASS_THRU_PROTOCOL PassThru;
>

These look fine.

(8) A general request regarding your git setup: please run the
"BaseTools/Scripts/SetupGit.py" script in your edk2 clone.

The reason I'm asking for that right now is that the script will point
the "diff.orderFile" setting to "BaseTools/Conf/diff.order". And that
will make git-format-patch, on your end, place the header file changes
ahead of the C file changes, in the generated emails.

It helps reviewers greatly if they can first see the declarative changes
(such as new types, new structure members, and so on), before they face
the code using the new constructs.

The script in question configures a bunch of other cool stuff too that
boosts reviewer productivity.

Thanks,
Laszlo