Messages in this thread Patch in this message | | | Subject | Re: [PATCH 11/13] dma-direct: handle the memory encryption bit in common code | From | Tom Lendacky <> | Date | Wed, 14 Mar 2018 10:44:29 -0500 |
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On 03/13/2018 08:10 AM, Christoph Hellwig wrote: > On Mon, Mar 12, 2018 at 02:48:51PM -0500, Tom Lendacky wrote: >> Ok, I found one issue that allows this to work when the IOMMU isn't >> enabled (see below). > > Thanks, folded! > >> But the bigger issue is when the IOMMU is enabled. The IOMMU code uses >> a common mapping routine to create the I/O page tables. This routine >> assumes that all memory being mapped is encrypted and therefore sets the >> encryption bit in the I/O page tables. With this patch, the call to >> dma_alloc_direct() now returns un-encrypted memory which results in an >> encryption mis-match. I think keeping dma_alloc_direct() as it was prior >> to this patch is the way to go. It allows SME DMA allocations to remain >> encrypted and avoids added complexity in the amd_iommu.c file. This >> would mean that SEV would still have special DMA operations (so that the >> alloc/free can change the memory to un-encrypted). >> >> What do you think? > > In terms of logic you are right. I still don't like keeping a just > slightly tweaked version of dma_alloc_direct around just for this, it > will be perpetually out of sync in terms of features and bug fixes. > > What do you think about this version that does the decision at runtime: > > http://git.infradead.org/users/hch/misc.git/commitdiff/b89f24dc856595dc7610d672bf077195ab0dabf4 > > The full tree is available here for testing: > > git://git.infradead.org/users/hch/misc.git dma-direct-x86 >
Thanks for the pointer to the tree. I did find one bug in the allocation routine, that once fixed (see below), worked with SME for IOMMU on and off and worked with an SEV guest.
I understand the comment about using sev_active() in the dma-direct code, maybe we can up with something later to address that.
Thanks, Tom
diff --git a/lib/dma-direct.c b/lib/dma-direct.c index 856e140..988a3d8 100644 --- a/lib/dma-direct.c +++ b/lib/dma-direct.c @@ -82,10 +82,12 @@ void *dma_direct_alloc(struct device *dev, size_t size, dma_addr_t *dma_handle,
if (!page) return NULL; - *dma_handle = __phys_to_dma(dev, page_to_phys(page)); + *dma_handle = phys_to_dma(dev, page_to_phys(page)); ret = page_address(page); - if (sev_active()) + if (sev_active()) { + *dma_handle = __phys_to_dma(dev, page_to_phys(page)); set_memory_decrypted((unsigned long)ret, 1 << page_order); + } memset(ret, 0, size); return ret; }
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