From 9ed745b96746dedc23a86c66ebb2beedd65471a6 Mon Sep 17 00:00:00 2001 From: Laszlo Ersek Date: Thu, 7 Sep 2017 15:30:19 +0200 Subject: [PATCH] OvmfPkg/IoMmuDxe: track all mappings The "mRecycledMapInfos" list implements an internal pool of unused MAP_INFO structures between the IoMmuUnmap() and IoMmuMap() functions. The original goal was to allow IoMmuUnmap() to tear down CommonBuffer mappings without releasing any memory: IoMmuUnmap() would recycle the MAP_INFO structure to the list, and IoMmuMap() would always check the list first, before allocating a brand new MAP_INFO structure. In one of the following patches, we'll change OvmfPkg/IoMmuDxe so that it unmaps all existent bus master operations (CommonBuffer, Read, Write) at ExitBootServices(), strictly after the individual device drivers abort pending DMA on the devices they manage, in their own ExitBootServices() notification functions. For this, rename and repurpose the list to track all live mappings. This means that IoMmuUnmap() will always release a MAP_INFO structure (even when cleaning up a CommonBuffer operation). That's fine (for now), because device drivers are no longer expected to call Unmap() in their ExitBootServices() notification functions. In theory, we could also move the allocation and freeing of the stash buffer from IoMmuAllocateBuffer() and IoMmuFreeBuffer(), respectively, to IoMmuMap() and IoMmuUnmap(). However, this would require allocating and freeing a stash buffer in *both* IoMmuMap() and IoMmuUnmap(), as IoMmuMap() performs in-place decryption for CommonBuffer operations, and IoMmuUnmap() performs in-place encryption for the same. By keeping the stash buffer allocation as-is, not only do we keep the code almost fully undisturbed, but - we also continue to guarantee that IoMmuUnmap() succeeds: allocating a stash buffer in IoMmuUnmap(), for in-place encryption after a CommonBuffer operation, could fail; - we also keep IoMmuUnmap() largely reusable for ExitBootServices() callback context: allocating a stash buffer in IoMmuUnmap() would simply be forbidden in that context. Cc: Ard Biesheuvel Cc: Brijesh Singh Cc: Jiewen Yao Cc: Jordan Justen Contributed-under: TianoCore Contribution Agreement 1.1 Signed-off-by: Laszlo Ersek Reviewed-by: Jiewen Yao Reviewed-by: Ard Biesheuvel Reviewed-by: Brijesh Singh Tested-by: Brijesh Singh --- OvmfPkg/IoMmuDxe/AmdSevIoMmu.c | 49 +++++++++++++--------------------- 1 file changed, 18 insertions(+), 31 deletions(-) diff --git a/OvmfPkg/IoMmuDxe/AmdSevIoMmu.c b/OvmfPkg/IoMmuDxe/AmdSevIoMmu.c index bc57de5b57..c86e734985 100644 --- a/OvmfPkg/IoMmuDxe/AmdSevIoMmu.c +++ b/OvmfPkg/IoMmuDxe/AmdSevIoMmu.c @@ -33,14 +33,11 @@ typedef struct { } MAP_INFO; // -// List of MAP_INFO structures recycled by Unmap(). +// List of the MAP_INFO structures that have been set up by IoMmuMap() and not +// yet torn down by IoMmuUnmap(). The list represents the full set of mappings +// currently in effect. // -// Recycled MAP_INFO structures are equally good for future recycling and -// freeing. -// -STATIC LIST_ENTRY mRecycledMapInfos = INITIALIZE_LIST_HEAD_VARIABLE ( - mRecycledMapInfos - ); +STATIC LIST_ENTRY mMapInfos = INITIALIZE_LIST_HEAD_VARIABLE (mMapInfos); #define COMMON_BUFFER_SIG SIGNATURE_64 ('C', 'M', 'N', 'B', 'U', 'F', 'F', 'R') @@ -123,7 +120,6 @@ IoMmuMap ( ) { EFI_STATUS Status; - LIST_ENTRY *RecycledMapInfo; MAP_INFO *MapInfo; EFI_ALLOCATE_TYPE AllocateType; COMMON_BUFFER_HEADER *CommonBufferHeader; @@ -150,19 +146,10 @@ IoMmuMap ( // Allocate a MAP_INFO structure to remember the mapping when Unmap() is // called later. // - RecycledMapInfo = GetFirstNode (&mRecycledMapInfos); - if (RecycledMapInfo == &mRecycledMapInfos) { - // - // No recycled MAP_INFO structure, allocate a new one. - // - MapInfo = AllocatePool (sizeof (MAP_INFO)); - if (MapInfo == NULL) { - Status = EFI_OUT_OF_RESOURCES; - goto Failed; - } - } else { - MapInfo = CR (RecycledMapInfo, MAP_INFO, Link, MAP_INFO_SIG); - RemoveEntryList (RecycledMapInfo); + MapInfo = AllocatePool (sizeof (MAP_INFO)); + if (MapInfo == NULL) { + Status = EFI_OUT_OF_RESOURCES; + goto Failed; } // @@ -298,6 +285,10 @@ IoMmuMap ( ); } + // + // Track all MAP_INFO structures. + // + InsertHeadList (&mMapInfos, &MapInfo->Link); // // Populate output parameters. // @@ -430,24 +421,20 @@ IoMmuUnmap ( CommonBufferHeader->StashBuffer, MapInfo->NumberOfBytes ); - - // - // Recycle the MAP_INFO structure. - // - InsertTailList (&mRecycledMapInfos, &MapInfo->Link); } else { ZeroMem ( (VOID *)(UINTN)MapInfo->PlainTextAddress, EFI_PAGES_TO_SIZE (MapInfo->NumberOfPages) ); gBS->FreePages (MapInfo->PlainTextAddress, MapInfo->NumberOfPages); - - // - // Free the MAP_INFO structure. - // - FreePool (MapInfo); } + // + // Forget and free the MAP_INFO structure. + // + RemoveEntryList (&MapInfo->Link); + FreePool (MapInfo); + return EFI_SUCCESS; } -- 2.39.2