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Message-ID: <20160912105815.3z5bvzbcfjcj4ku7@pd.tnic>
Date: Mon, 12 Sep 2016 12:58:15 +0200
From: Borislav Petkov <bp@...en8.de>
To: Tom Lendacky <thomas.lendacky@....com>
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 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...
> +{
> + 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 ...
> + * 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.
> +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.
> +}
> +
> int __init swiotlb_init_with_tbl(char *tlb, unsigned long nslabs, int verbose)
> {
> void *v_overflow_buffer;
--
Regards/Gruss,
Boris.
ECO tip #101: Trim your mails when you reply.
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