Re: [RFC PATCH v4 18/28] x86: DMA support for memory encryption

Tom Lendacky
2017-03-06T19:25:33Z

On 2/25/2017 11:10 AM, Borislav Petkov wrote:
> On Thu, Feb 16, 2017 at 09:46:04AM -0600, Tom Lendacky wrote:
>> Since DMA addresses will effectively look like 48-bit addresses when the
>> memory encryption mask is set, SWIOTLB is needed if the DMA mask of the
>> device performing the DMA does not support 48-bits. SWIOTLB will be
>> initialized to create decrypted bounce buffers for use by these devices.
>>
>> Signed-off-by: Tom Lendacky <thomas.lendacky@amd.com>
>> ---
>
> Just nitpicks below...
>
>> diff --git a/arch/x86/mm/mem_encrypt.c b/arch/x86/mm/mem_encrypt.c
>> index ec548e9..a46bcf4 100644
>> --- a/arch/x86/mm/mem_encrypt.c
>> +++ b/arch/x86/mm/mem_encrypt.c
>> @@ -13,11 +13,14 @@
>> #include <linux/linkage.h>
>> #include <linux/init.h>
>> #include <linux/mm.h>
>> +#include <linux/dma-mapping.h>
>> +#include <linux/swiotlb.h>
>>
>> #include <asm/tlbflush.h>
>> #include <asm/fixmap.h>
>> #include <asm/setup.h>
>> #include <asm/bootparam.h>
>> +#include <asm/cacheflush.h>
>>
>> extern pmdval_t early_pmd_flags;
>> int __init __early_make_pgtable(unsigned long, pmdval_t);
>> @@ -192,3 +195,22 @@ void __init sme_early_init(void)
>> for (i = 0; i < ARRAY_SIZE(protection_map); i++)
>> protection_map[i] = pgprot_encrypted(protection_map[i]);
>> }
>> +
>> +/* Architecture __weak replacement functions */
>> +void __init mem_encrypt_init(void)
>> +{
>> + if (!sme_me_mask)
>
> !sme_active()
>
> no?

I was probably looking ahead to SEV on this one. Basically if the
sme_me_mask is non-zero we will want to make SWIOTLB decrypted.

>
> Unless we're going to be switching SME dynamically at run time?
>
>> + return;
>> +
>> + /* Call into SWIOTLB to update the SWIOTLB DMA buffers */
>> + swiotlb_update_mem_attributes();
>> +}
>> +
>> +void swiotlb_set_mem_attributes(void *vaddr, unsigned long size)
>> +{
>> + WARN(PAGE_ALIGN(size) != size,
>> + "size is not page aligned (%#lx)\n", size);
>
> "page-aligned" I guess.

Ok.

>
>> +
>> + /* Make the SWIOTLB buffer area decrypted */
>> + set_memory_decrypted((unsigned long)vaddr, size >> PAGE_SHIFT);
>> +}
>> diff --git a/include/linux/swiotlb.h b/include/linux/swiotlb.h
>> index 4ee479f..15e7160 100644
>> --- a/include/linux/swiotlb.h
>> +++ b/include/linux/swiotlb.h
>> @@ -35,6 +35,7 @@ enum swiotlb_force {
>> extern unsigned long swiotlb_nr_tbl(void);
>> unsigned long swiotlb_size_or_default(void);
>> extern int swiotlb_late_init_with_tbl(char *tlb, unsigned long nslabs);
>> +extern void __init swiotlb_update_mem_attributes(void);
>>
>> /*
>> * Enumeration for sync targets
>> diff --git a/init/main.c b/init/main.c
>> index 8222caa..ba13f8f 100644
>> --- a/init/main.c
>> +++ b/init/main.c
>> @@ -466,6 +466,10 @@ void __init __weak thread_stack_cache_init(void)
>> }
>> #endif
>>
>> +void __init __weak mem_encrypt_init(void)
>> +{
>> +}
>> +
>> /*
>> * Set up kernel memory allocators
>> */
>> @@ -614,6 +618,15 @@ asmlinkage __visible void __init start_kernel(void)
>> */
>> locking_selftest();
>>
>> + /*
>> + * This needs to be called before any devices perform DMA
>> + * operations that might use the swiotlb bounce buffers.
>
> SWIOTLB

Ok.

>
>> + * This call will mark the bounce buffers as decrypted so
>> + * that their usage will not cause "plain-text" data to be
>> + * decrypted when accessed.
>> + */
>> + mem_encrypt_init();
>> +
>> #ifdef CONFIG_BLK_DEV_INITRD
>> if (initrd_start && !initrd_below_start_ok &&
>> page_to_pfn(virt_to_page((void *)initrd_start)) < min_low_pfn) {
>> diff --git a/lib/swiotlb.c b/lib/swiotlb.c
>> index a8d74a7..c463067 100644
>> --- a/lib/swiotlb.c
>> +++ b/lib/swiotlb.c
>> @@ -30,6 +30,7 @@
>> #include <linux/highmem.h>
>> #include <linux/gfp.h>
>> #include <linux/scatterlist.h>
>> +#include <linux/mem_encrypt.h>
>>
>> #include <asm/io.h>
>> #include <asm/dma.h>
>> @@ -155,6 +156,17 @@ unsigned long swiotlb_size_or_default(void)
>> return size ? size : (IO_TLB_DEFAULT_SIZE);
>> }
>>
>> +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 phys_to_dma(hwdev, address) & ~sme_me_mask;
>> +}
>> +
>> /* Note that this doesn't work with highmem page */
>> static dma_addr_t swiotlb_virt_to_bus(struct device *hwdev,
>> volatile void *address)
>> @@ -183,6 +195,31 @@ void swiotlb_print_info(void)
>> bytes >> 20, vstart, vend - 1);
>> }
>>
>> +/*
>> + * Early SWIOTLB allocation may be to early to allow an architecture to
>
> too

Yup.

>
>> + * perform the desired operations. This function allows the architecture to
>> + * call SWIOTLB when the operations are possible. This function needs to be
>
> s/This function/It/

Ok.

Thanks,
Tom

>
>> + * called before the SWIOTLB memory is used.
>> + */
>> +void __init swiotlb_update_mem_attributes(void)
>> +{
>> + void *vaddr;
>> + unsigned long bytes;
>> +
>> + if (no_iotlb_memory || late_alloc)
>> + return;
>> +
>> + vaddr = phys_to_virt(io_tlb_start);
>> + bytes = PAGE_ALIGN(io_tlb_nslabs << IO_TLB_SHIFT);
>> + swiotlb_set_mem_attributes(vaddr, bytes);
>> + memset(vaddr, 0, bytes);
>> +
>> + vaddr = phys_to_virt(io_tlb_overflow_buffer);
>> + bytes = PAGE_ALIGN(io_tlb_overflow);
>> + swiotlb_set_mem_attributes(vaddr, bytes);
>> + memset(vaddr, 0, bytes);
>> +}
>> +
>> int __init swiotlb_init_with_tbl(char *tlb, unsigned long nslabs, int verbose)
>> {
>> void *v_overflow_buffer;
>