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

[Tom Lendacky]

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@xxxxxxx>
> > ---
>
> 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;