> On 27 Jul 2017, at 21:55, Brijesh Singh <brijesh.si...@amd.com> wrote: > > > > On 07/27/2017 02:00 PM, Brijesh Singh wrote: > >>>> This distribution of operations seems wrong. The key point is that >>>> AllocateBuffer() *need not* result in a buffer that is immediately >>>> usable, and that client code is required to call Map() >>>> *unconditionally*, even if BusMasterCommonBuffer is the desired >>>> operation. Therefore, the right distribution of operations is: >>>> >>>> - IoMmuAllocateBuffer() allocates pages and does not touch the >>>> encryption mask.. >>>> >>>> - IoMmuFreeBuffer() deallocates pages and does not touch the encryption >>>> mask. >>>> >> Actually one of main reason why we cleared and restored the memory >> encryption mask >> during allocate/free is because we also consume the IOMMU protocol in >> QemuFwCfgLib >> as a method to allocate and free a DMA buffer. I am certainly open to >> suggestions. >> [1] >> https://github.com/tianocore/edk2/blob/master/OvmfPkg/Library/QemuFwCfgLib/QemuFwCfgDxe.c#L159 >> [2] >> https://github.com/tianocore/edk2/blob/master/OvmfPkg/Library/QemuFwCfgLib/QemuFwCfgDxe.c#L197 >>>> - IoMmuMap() does not allocate pages when BusMasterCommonBuffer is >>>> requested, and it allocates pages (bounce buffer) otherwise. >>>> >> I am trying to wrap my head around how we can support BusMasterCommonBuffer >> when buffer was not allocated by us. Changing the memory encryption mask in >> a page table will not update the contents. Also since the memory encryption >> mask works on PAGE_SIZE hence changing the encryption mask on not our >> allocated >> buffer could mess things up (e.g if NumberOfBytes is not PAGE_SIZE aligned). > > I may be missing something in my understanding. Here is a flow I have in my > mind, please correct me. > > OvmfPkg/VirtIoBlk.c: > > VirtioBlkInit() > .... > .... > VirtioRingInit > Virtio->AllocateSharedPages(RingSize, &Ring->Base) > PciIo->AllocatePages(RingSize, &RingAddress) > Virtio->MapSharedPages(...,BusMasterCommonBuffer, Ring->Base, RingSize, > &RingDeviceAddress) > ..... > ..... > > This case is straight forward and we can easily maps. No need for bounce > buffering. > > VirtioBlkReadBlocks(..., BufferSize, Buffer,) > ...... > ...... > SynchronousRequest(..., BufferSize, Buffer) > .... > Virtio->MapSharedPages(..., BusMasterCommonBuffer, Buffer, BufferSize, > &DeviceAddress) > VirtioAppendDesc(DeviceAddress, BufferSize, ...) > VirtioFlush (...) > > In the above case, "Buffer" was not allocated by us hence we will not able to > change the > memory encryption attributes. Am I missing something in the flow ? >
Common buffer mappings may only be created from buffers that were allocated by AllocateBuffer(). In fact, that is its main purpose > >>>> *Regardless* of BusMaster operation, the following actions are carried >>>> out unconditionally: >>>> >>>> . the memory encryption mask is cleared in this function (and in this >>>> function only), >>>> >>>> . An attempt is made to grab a MAP_INFO structure from an internal >>>> free list (to be introduced!). The head of the list is a new static >>>> variable. If the free list is empty, then a MAP_INFO structure is >>>> allocated with AllocatePool(). The NO_MAPPING macro becomes unused >>>> and can be deleted from the source code. >>>> >>>> - IoMmuUnmap() clears the encryption mask unconditionally. (For this, it >>>> has to consult the MAP_INFO structure that is being passed in from the >>>> caller.) In addition: >>>> >>>> . If MapInfo->Operation is BusMasterCommonBuffer, then we know the >>>> allocation was done separately in AllocateBuffer, so we do not >>>> release the pages. Otherwise, we do release the pages. >>>> >>>> . MapInfo is linked back on the internal free list (see above). It is >>>> *never* released with FreePool(). >>>> >>>> This approach guarantees that IoMmuUnmap() can de-program the IOMMU (= >>>> re-set the memory encryption mask) without changing the UEFI memory >>>> map. (I trust that MemEncryptSevSetPageEncMask() will not split page >>>> tables internally when it *re*sets the encryption mask -- is that >>>> correct?) > > > _______________________________________________ edk2-devel mailing list edk2-devel@lists.01.org https://lists.01.org/mailman/listinfo/edk2-devel
