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Date: Wed, 14 Sep 2016 08:36:30 -0500
From: Tom Lendacky <thomas.lendacky@....com>
To: Borislav Petkov <bp@...en8.de>
CC: <linux-arch@...r.kernel.org>, <linux-efi@...r.kernel.org>,
<kvm@...r.kernel.org>, <linux-doc@...r.kernel.org>,
<x86@...nel.org>, <linux-kernel@...r.kernel.org>,
<kasan-dev@...glegroups.com>, <linux-mm@...ck.org>,
<iommu@...ts.linux-foundation.org>,
Radim Krčmář <rkrcmar@...hat.com>,
Arnd Bergmann <arnd@...db.de>,
Jonathan Corbet <corbet@....net>,
Matt Fleming <matt@...eblueprint.co.uk>,
Joerg Roedel <joro@...tes.org>,
Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
Andrey Ryabinin <aryabinin@...tuozzo.com>,
Ingo Molnar <mingo@...hat.com>,
Andy Lutomirski <luto@...nel.org>,
"H. Peter Anvin" <hpa@...or.com>,
Paolo Bonzini <pbonzini@...hat.com>,
Alexander Potapenko <glider@...gle.com>,
Thomas Gleixner <tglx@...utronix.de>,
Dmitry Vyukov <dvyukov@...gle.com>
Subject: Re: [RFC PATCH v2 14/20] x86: DMA support for memory encryption
On 09/12/2016 05:58 AM, Borislav Petkov wrote:
> On Mon, Aug 22, 2016 at 05:38:07PM -0500, 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 un-encrypted bounce buffers for use by these devices.
>>
>> Signed-off-by: Tom Lendacky <thomas.lendacky@....com>
>> ---
>> arch/x86/include/asm/dma-mapping.h | 5 ++-
>> arch/x86/include/asm/mem_encrypt.h | 6 +++
>> arch/x86/kernel/pci-dma.c | 11 ++++--
>> arch/x86/kernel/pci-nommu.c | 2 +
>> arch/x86/kernel/pci-swiotlb.c | 8 +++--
>> arch/x86/mm/mem_encrypt.c | 22 ++++++++++++
>> include/linux/swiotlb.h | 1 +
>> init/main.c | 13 +++++++
>> lib/swiotlb.c | 64 ++++++++++++++++++++++++++++++++----
>> 9 files changed, 115 insertions(+), 17 deletions(-)
>
> ...
>
>> @@ -172,3 +174,23 @@ void __init sme_early_init(void)
>> for (i = 0; i < ARRAY_SIZE(protection_map); i++)
>> protection_map[i] = __pgprot(pgprot_val(protection_map[i]) | sme_me_mask);
>> }
>> +
>> +/* Architecture __weak replacement functions */
>> +void __init mem_encrypt_init(void)
>> +{
>> + if (!sme_me_mask)
>> + return;
>> +
>> + /* Make SWIOTLB use an unencrypted DMA area */
>> + swiotlb_clear_encryption();
>> +}
>> +
>> +unsigned long swiotlb_get_me_mask(void)
>
> This could just as well be named to something more generic:
>
> swiotlb_get_clear_dma_mask() or so which basically means the mask of
> bits which get cleared before returning DMA addresses...
Ok.
>
>> +{
>> + return sme_me_mask;
>> +}
>> +
>> +void swiotlb_set_mem_dec(void *vaddr, unsigned long size)
>> +{
>> + sme_set_mem_dec(vaddr, size);
>> +}
>> diff --git a/include/linux/swiotlb.h b/include/linux/swiotlb.h
>> index 5f81f8a..5c909fc 100644
>> --- a/include/linux/swiotlb.h
>> +++ b/include/linux/swiotlb.h
>> @@ -29,6 +29,7 @@ int swiotlb_init_with_tbl(char *tlb, unsigned long nslabs, int verbose);
>> 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_clear_encryption(void);
>>
>> /*
>> * Enumeration for sync targets
>> diff --git a/init/main.c b/init/main.c
>> index a8a58e2..82c7cd9 100644
>> --- a/init/main.c
>> +++ b/init/main.c
>> @@ -458,6 +458,10 @@ void __init __weak thread_stack_cache_init(void)
>> }
>> #endif
>>
>> +void __init __weak mem_encrypt_init(void)
>> +{
>> +}
>> +
>> /*
>> * Set up kernel memory allocators
>> */
>> @@ -598,6 +602,15 @@ 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.
>> + * This call will mark the bounce buffers as un-encrypted so
>> + * that the usage of them will not cause "plain-text" data
>
> ...that their usage will not cause ...
Ok.
>
>> + * 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 22e13a0..15d5741 100644
>> --- a/lib/swiotlb.c
>> +++ b/lib/swiotlb.c
>> @@ -131,6 +131,26 @@ unsigned long swiotlb_size_or_default(void)
>> return size ? size : (IO_TLB_DEFAULT_SIZE);
>> }
>>
>> +/*
>> + * Support for memory encryption. If memory encryption is supported, then an
>> + * override to these functions will be provided.
>> + */
>
> No need for that comment.
Ok.
>
>> +unsigned long __weak swiotlb_get_me_mask(void)
>> +{
>> + return 0;
>> +}
>> +
>> +void __weak swiotlb_set_mem_dec(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) & ~swiotlb_get_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)
>> @@ -159,6 +179,30 @@ void swiotlb_print_info(void)
>> bytes >> 20, vstart, vend - 1);
>> }
>>
>> +/*
>> + * If memory encryption is active, the DMA address for an encrypted page may
>> + * be beyond the range of the device. If bounce buffers are required be sure
>> + * that they are not on an encrypted page. This should be called before the
>> + * iotlb area is used.
>> + */
>> +void __init swiotlb_clear_encryption(void)
>> +{
>> + void *vaddr;
>> + unsigned long bytes;
>> +
>> + if (no_iotlb_memory || !io_tlb_start || late_alloc)
>> + return;
>> +
>> + vaddr = phys_to_virt(io_tlb_start);
>> + bytes = PAGE_ALIGN(io_tlb_nslabs << IO_TLB_SHIFT);
>> + swiotlb_set_mem_dec(vaddr, bytes);
>> + memset(vaddr, 0, bytes);
>
> io_tlb_start is cleared...
>
>> +
>> + vaddr = phys_to_virt(io_tlb_overflow_buffer);
>> + bytes = PAGE_ALIGN(io_tlb_overflow);
>> + swiotlb_set_mem_dec(vaddr, bytes);
>
> ... but io_tlb_overflow_buffer isn't? I don't see the difference here.
Yup, I missed that one. Will memset this as well.
Thanks,
Tom
>
>> +}
>> +
>> int __init swiotlb_init_with_tbl(char *tlb, unsigned long nslabs, int verbose)
>> {
>> void *v_overflow_buffer;
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