| lists.openwall.net | lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC | |
|
Open Source and information security mailing list archives
| ||
|
Message-ID: <502fa745-ddad-f91b-52bc-52edecf8fdbc@arm.com>
Date: Thu, 20 Feb 2020 17:21:35 +0000
From: Robin Murphy <robin.murphy@....com>
To: Christoph Hellwig <hch@....de>, Jonas Bonn <jonas@...thpole.se>,
Stefan Kristiansson <stefan.kristiansson@...nalahti.fi>,
Stafford Horne <shorne@...il.com>
Cc: Marek Szyprowski <m.szyprowski@...sung.com>,
Will Deacon <will@...nel.org>,
Mark Rutland <mark.rutland@....com>,
openrisc@...ts.librecores.org, iommu@...ts.linux-foundation.org,
linux-arm-kernel@...ts.infradead.org, linux-arch@...r.kernel.org,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] dma-mapping: support setting memory uncached in place
On 20/02/2020 5:01 pm, Christoph Hellwig wrote:
> We currently only support remapping memory as uncached through vmap
> or a magic uncached segment provided by some architectures. But there
> is a simpler and much better way available on some architectures where
> we can just remap the memory in place. The advantages are:
>
> 1) no aliasing is possible, which prevents speculating into the
> cached alias
> 2) there is no need to allocate new ptes and thus no need for a special
> pre-allocated pool of memory that can be used with GFP_ATOMIC DMA
> allocations
>
> The downside is that architectures must provide a way to set arbitrary
> pages uncached in the kernel mapping, which might not be possible on
> architecture that have a special implicit kernel mapping, and requires
> splitting of huge page kernel mappings where they exist.
>
> Signed-off-by: Christoph Hellwig <hch@....de>
> ---
> include/linux/dma-noncoherent.h | 3 +++
> kernel/dma/Kconfig | 8 ++++++++
> kernel/dma/direct.c | 28 ++++++++++++++++++----------
> 3 files changed, 29 insertions(+), 10 deletions(-)
>
> diff --git a/include/linux/dma-noncoherent.h b/include/linux/dma-noncoherent.h
> index ca9b5770caee..0820ec58f119 100644
> --- a/include/linux/dma-noncoherent.h
> +++ b/include/linux/dma-noncoherent.h
> @@ -111,4 +111,7 @@ static inline void arch_dma_prep_coherent(struct page *page, size_t size)
> void *uncached_kernel_address(void *addr);
> void *cached_kernel_address(void *addr);
>
> +int arch_dma_set_uncached(void *cpu_addr, size_t size);
> +void arch_dma_clear_uncached(void *cpu_addr, size_t size);
> +
> #endif /* _LINUX_DMA_NONCOHERENT_H */
> diff --git a/kernel/dma/Kconfig b/kernel/dma/Kconfig
> index 4c103a24e380..7bc0b77f1243 100644
> --- a/kernel/dma/Kconfig
> +++ b/kernel/dma/Kconfig
> @@ -83,6 +83,14 @@ config DMA_DIRECT_REMAP
> bool
> select DMA_REMAP
>
> +#
> +# Should be selected if the architecture can remap memory from the page
> +# allocator and CMA as uncached and provides the arch_dma_set_uncached and
> +# arch_dma_clear_uncached helpers
> +#
> +config ARCH_HAS_DMA_SET_UNCACHED
> + bool
> +
> config DMA_CMA
> bool "DMA Contiguous Memory Allocator"
> depends on HAVE_DMA_CONTIGUOUS && CMA
> diff --git a/kernel/dma/direct.c b/kernel/dma/direct.c
> index 6af7ae83c4ad..73fe65a4cbc0 100644
> --- a/kernel/dma/direct.c
> +++ b/kernel/dma/direct.c
> @@ -169,11 +169,8 @@ void *dma_direct_alloc_pages(struct device *dev, size_t size,
> ret = dma_common_contiguous_remap(page, PAGE_ALIGN(size),
> dma_pgprot(dev, PAGE_KERNEL, attrs),
> __builtin_return_address(0));
> - if (!ret) {
> - dma_free_contiguous(dev, page, size);
> - return ret;
> - }
> -
> + if (!ret)
> + goto out_free_pages;
> memset(ret, 0, size);
> goto done;
> }
> @@ -186,8 +183,7 @@ void *dma_direct_alloc_pages(struct device *dev, size_t size,
> * so log an error and fail.
> */
> dev_info(dev, "Rejecting highmem page from CMA.\n");
> - dma_free_contiguous(dev, page, size);
> - return NULL;
> + goto out_free_pages;
> }
>
> ret = page_address(page);
> @@ -196,10 +192,15 @@ void *dma_direct_alloc_pages(struct device *dev, size_t size,
>
> memset(ret, 0, size);
>
> - if (IS_ENABLED(CONFIG_ARCH_HAS_UNCACHED_SEGMENT) &&
> - dma_alloc_need_uncached(dev, attrs)) {
> + if (dma_alloc_need_uncached(dev, attrs)) {
> arch_dma_prep_coherent(page, size);
> - ret = uncached_kernel_address(ret);
> +
> + if (IS_ENABLED(CONFIG_ARCH_HAS_DMA_SET_UNCACHED)) {
> + if (!arch_dma_set_uncached(ret, size))
> + goto out_free_pages;
> + } else if (IS_ENABLED(CONFIG_ARCH_HAS_UNCACHED_SEGMENT)) {
> + ret = uncached_kernel_address(ret);
Hmm, would we actually need to keep ARCH_HAS_UNCACHED_SEGMENT? If
arch_dma_set_uncached() returned void*/ERR_PTR instead, then it could
work for both cases (with arch_dma_clear_uncached() being a no-op for
segments).
Robin.
> + }
> }
> done:
> if (force_dma_unencrypted(dev))
> @@ -207,6 +208,9 @@ void *dma_direct_alloc_pages(struct device *dev, size_t size,
> else
> *dma_handle = phys_to_dma(dev, page_to_phys(page));
> return ret;
> +out_free_pages:
> + dma_free_contiguous(dev, page, size);
> + return NULL;
> }
>
> void dma_direct_free_pages(struct device *dev, size_t size, void *cpu_addr,
> @@ -230,6 +234,8 @@ void dma_direct_free_pages(struct device *dev, size_t size, void *cpu_addr,
>
> if (IS_ENABLED(CONFIG_DMA_REMAP) && is_vmalloc_addr(cpu_addr))
> vunmap(cpu_addr);
> + else if (IS_ENABLED(CONFIG_ARCH_HAS_DMA_SET_UNCACHED))
> + arch_dma_clear_uncached(cpu_addr, size);
>
> dma_free_contiguous(dev, dma_direct_to_page(dev, dma_addr), size);
> }
> @@ -238,6 +244,7 @@ void *dma_direct_alloc(struct device *dev, size_t size,
> dma_addr_t *dma_handle, gfp_t gfp, unsigned long attrs)
> {
> if (!IS_ENABLED(CONFIG_ARCH_HAS_UNCACHED_SEGMENT) &&
> + !IS_ENABLED(CONFIG_ARCH_HAS_DMA_SET_UNCACHED) &&
> !IS_ENABLED(CONFIG_DMA_DIRECT_REMAP) &&
> dma_alloc_need_uncached(dev, attrs))
> return arch_dma_alloc(dev, size, dma_handle, gfp, attrs);
> @@ -248,6 +255,7 @@ void dma_direct_free(struct device *dev, size_t size,
> void *cpu_addr, dma_addr_t dma_addr, unsigned long attrs)
> {
> if (!IS_ENABLED(CONFIG_ARCH_HAS_UNCACHED_SEGMENT) &&
> + !IS_ENABLED(CONFIG_ARCH_HAS_DMA_SET_UNCACHED) &&
> !IS_ENABLED(CONFIG_DMA_DIRECT_REMAP) &&
> dma_alloc_need_uncached(dev, attrs))
> arch_dma_free(dev, size, cpu_addr, dma_addr, attrs);
>
Powered by blists - more mailing lists