Re: [PATCH 11/13] dma-direct: handle the memory encryption bit in common code

Tom Lendacky
2018-03-12T19:49:00Z

On 3/12/2018 1:29 PM, Tom Lendacky wrote:
> On 3/5/2018 11:46 AM, Christoph Hellwig wrote:
>> Give the basic phys_to_dma and dma_to_phys helpers a __-prefix and add
>> the memory encryption mask to the non-prefixed versions. Use the
>> __-prefixed versions directly instead of clearing the mask again in
>> various places.
>>
>> With that in place the generic dma-direct routines can be used to
>> allocate non-encrypted bounce buffers, and the x86 SEV case can use
>> the generic swiotlb ops.
>>
>> Signed-off-by: Christoph Hellwig <hch@lst.de>
>
> So this patch results in my system failing to boot when SME is active.
> I'm investigating further to see why. I'll follow up with more details
> as I find them.

Ok, I found one issue that allows this to work when the IOMMU isn't
enabled (see below).

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?

>
> Additionally, when running with SME (not SEV), this is forcing all DMA
> coherent allocations to be decrypted, when that isn't required with SME
> (as long as the device can perform 48-bit or greater DMA). So it may
> be worth looking at only doing the decrypted allocations for SEV.
>
> Thanks,
> Tom
>
>> ---
>> arch/arm/include/asm/dma-direct.h | 4 +-
>> arch/mips/cavium-octeon/dma-octeon.c | 10 +--
>> .../include/asm/mach-cavium-octeon/dma-coherence.h | 4 +-
>> .../include/asm/mach-loongson64/dma-coherence.h | 10 +--
>> arch/mips/loongson64/common/dma-swiotlb.c | 4 +-
>> arch/powerpc/include/asm/dma-direct.h | 4 +-
>> arch/x86/Kconfig | 2 +-
>> arch/x86/include/asm/dma-direct.h | 25 +-------
>> arch/x86/mm/mem_encrypt.c | 73 +---------------------
>> arch/x86/pci/sta2x11-fixup.c | 6 +-
>> include/linux/dma-direct.h | 21 ++++++-
>> lib/dma-direct.c | 21 +++++--
>> lib/swiotlb.c | 25 +++-----
>> 13 files changed, 70 insertions(+), 139 deletions(-)
>>

< ... SNIP ... >

>> diff --git a/lib/dma-direct.c b/lib/dma-direct.c
>> index c9e8e21cb334..84f50b5982fc 100644
>> --- a/lib/dma-direct.c
>> +++ b/lib/dma-direct.c
>> @@ -9,6 +9,7 @@
>> #include <linux/scatterlist.h>
>> #include <linux/dma-contiguous.h>
>> #include <linux/pfn.h>
>> +#include <linux/set_memory.h>
>>
>> #define DIRECT_MAPPING_ERROR 0
>>
>> @@ -35,9 +36,13 @@ check_addr(struct device *dev, dma_addr_t dma_addr, size_t size,
>> return true;
>> }
>>
>> +/*
>> + * Since we will be clearing the encryption bit, check the mask with it already
>> + * cleared.
>> + */
>> static bool dma_coherent_ok(struct device *dev, phys_addr_t phys, size_t size)
>> {
>> - return phys_to_dma(dev, phys) + size - 1 <= dev->coherent_dma_mask;
>> + return __phys_to_dma(dev, phys) + size - 1 <= dev->coherent_dma_mask;
>> }
>>
>> void *dma_direct_alloc(struct device *dev, size_t size, dma_addr_t *dma_handle,
>> @@ -46,6 +51,7 @@ void *dma_direct_alloc(struct device *dev, size_t size, dma_addr_t *dma_handle,
>> unsigned int count = PAGE_ALIGN(size) >> PAGE_SHIFT;
>> int page_order = get_order(size);
>> struct page *page = NULL;
>> + void *ret;
>>
>> /* GFP_DMA32 and GFP_DMA are no ops without the corresponding zones: */
>> if (dev->coherent_dma_mask <= DMA_BIT_MASK(ARCH_ZONE_DMA_BITS))
>> @@ -78,10 +84,11 @@ 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));
>> - memset(page_address(page), 0, size);
>> - return page_address(page);
>> + *dma_handle = __phys_to_dma(dev, page_to_phys(page));
>> + ret = page_address(page);
>> + set_memory_decrypted((unsigned long)ret, page_order);

The second parameter should be 1 << page_order to get the number of
pages.

Thanks,
Tom

>> + memset(ret, 0, size);
>> + return ret;
>> }
>>
>> /*
>> @@ -92,9 +99,11 @@ void dma_direct_free(struct device *dev, size_t size, void *cpu_addr,
>> dma_addr_t dma_addr, unsigned long attrs)
>> {
>> unsigned int count = PAGE_ALIGN(size) >> PAGE_SHIFT;
>> + unsigned int page_order = get_order(size);
>>
>> + set_memory_encrypted((unsigned long)cpu_addr, 1 << page_order);
>> if (!dma_release_from_contiguous(dev, virt_to_page(cpu_addr), count))
>> - free_pages((unsigned long)cpu_addr, get_order(size));
>> + free_pages((unsigned long)cpu_addr, page_order);
>> }
>>
>> static dma_addr_t dma_direct_map_page(struct device *dev, struct page *page,
>> diff --git a/lib/swiotlb.c b/lib/swiotlb.c
>> index c43ec2271469..ca8eeaead925 100644
>> --- a/lib/swiotlb.c
>> +++ b/lib/swiotlb.c
>> @@ -158,13 +158,6 @@ unsigned long swiotlb_size_or_default(void)
>>
>> void __weak swiotlb_set_mem_attributes(void *vaddr, unsigned long size) { }
>>
>> -/* For swiotlb, clear memory encryption mask from dma addresses */
>> -static dma_addr_t swiotlb_phys_to_dma(struct device *hwdev,
>> - phys_addr_t address)
>> -{
>> - return __sme_clr(phys_to_dma(hwdev, address));
>> -}
>> -
>> /* Note that this doesn't work with highmem page */
>> static dma_addr_t swiotlb_virt_to_bus(struct device *hwdev,
>> volatile void *address)
>> @@ -622,7 +615,7 @@ map_single(struct device *hwdev, phys_addr_t phys, size_t size,
>> return SWIOTLB_MAP_ERROR;
>> }
>>
>> - start_dma_addr = swiotlb_phys_to_dma(hwdev, io_tlb_start);
>> + start_dma_addr = __phys_to_dma(hwdev, io_tlb_start);
>> return swiotlb_tbl_map_single(hwdev, start_dma_addr, phys, size,
>> dir, attrs);
>> }
>> @@ -726,12 +719,12 @@ swiotlb_alloc_buffer(struct device *dev, size_t size, dma_addr_t *dma_handle,
>> goto out_warn;
>>
>> phys_addr = swiotlb_tbl_map_single(dev,
>> - swiotlb_phys_to_dma(dev, io_tlb_start),
>> + __phys_to_dma(dev, io_tlb_start),
>> 0, size, DMA_FROM_DEVICE, 0);
>> if (phys_addr == SWIOTLB_MAP_ERROR)
>> goto out_warn;
>>
>> - *dma_handle = swiotlb_phys_to_dma(dev, phys_addr);
>> + *dma_handle = __phys_to_dma(dev, phys_addr);
>> if (dma_coherent_ok(dev, *dma_handle, size))
>> goto out_unmap;
>>
>> @@ -867,10 +860,10 @@ dma_addr_t swiotlb_map_page(struct device *dev, struct page *page,
>> map = map_single(dev, phys, size, dir, attrs);
>> if (map == SWIOTLB_MAP_ERROR) {
>> swiotlb_full(dev, size, dir, 1);
>> - return swiotlb_phys_to_dma(dev, io_tlb_overflow_buffer);
>> + return __phys_to_dma(dev, io_tlb_overflow_buffer);
>> }
>>
>> - dev_addr = swiotlb_phys_to_dma(dev, map);
>> + dev_addr = __phys_to_dma(dev, map);
>>
>> /* Ensure that the address returned is DMA'ble */
>> if (dma_capable(dev, dev_addr, size))
>> @@ -879,7 +872,7 @@ dma_addr_t swiotlb_map_page(struct device *dev, struct page *page,
>> attrs |= DMA_ATTR_SKIP_CPU_SYNC;
>> swiotlb_tbl_unmap_single(dev, map, size, dir, attrs);
>>
>> - return swiotlb_phys_to_dma(dev, io_tlb_overflow_buffer);
>> + return __phys_to_dma(dev, io_tlb_overflow_buffer);
>> }
>>
>> /*
>> @@ -1009,7 +1002,7 @@ swiotlb_map_sg_attrs(struct device *hwdev, struct scatterlist *sgl, int nelems,
>> sg_dma_len(sgl) = 0;
>> return 0;
>> }
>> - sg->dma_address = swiotlb_phys_to_dma(hwdev, map);
>> + sg->dma_address = __phys_to_dma(hwdev, map);
>> } else
>> sg->dma_address = dev_addr;
>> sg_dma_len(sg) = sg->length;
>> @@ -1073,7 +1066,7 @@ swiotlb_sync_sg_for_device(struct device *hwdev, struct scatterlist *sg,
>> int
>> swiotlb_dma_mapping_error(struct device *hwdev, dma_addr_t dma_addr)
>> {
>> - return (dma_addr == swiotlb_phys_to_dma(hwdev, io_tlb_overflow_buffer));
>> + return (dma_addr == __phys_to_dma(hwdev, io_tlb_overflow_buffer));
>> }
>>
>> /*
>> @@ -1085,7 +1078,7 @@ swiotlb_dma_mapping_error(struct device *hwdev, dma_addr_t dma_addr)
>> int
>> swiotlb_dma_supported(struct device *hwdev, u64 mask)
>> {
>> - return swiotlb_phys_to_dma(hwdev, io_tlb_end - 1) <= mask;
>> + return __phys_to_dma(hwdev, io_tlb_end - 1) <= mask;
>> }
>>
>> #ifdef CONFIG_DMA_DIRECT_OPS
>>