Re: [rfc] dma-mapping: preallocate unencrypted DMA atomic pool

[Tom Lendacky]

On 12/31/19 7:54 PM, David Rientjes wrote:
> Christoph, Thomas, is something like this (without the diagnosic 
> information included in this patch) acceptable for these allocations?  
> Adding expansion support when the pool is half depleted wouldn't be *that* 
> hard.

Sorry for the delay in responding...  Overall, I think this will work
well. If you want the default size to be adjustable, you can always go
with a Kconfig setting or a command line parameter or both (I realize the
command line parameter is not optimal).

Just a couple of overall comments about the use of variable names and
messages using both unencrypted and encrypted, I think the use should be
consistent throughout the patch.

Thanks,
Tom

> 
> Or are there alternatives we should consider?  Thanks!
> 
> 
> 
> 
> When AMD SEV is enabled in the guest, all allocations through 
> dma_pool_alloc_page() must call set_memory_decrypted() for unencrypted 
> DMA.  This includes dma_pool_alloc() and dma_direct_alloc_pages().  These 
> calls may block which is not allowed in atomic allocation contexts such as 
> from the NVMe driver.
> 
> Preallocate a complementary unecrypted DMA atomic pool that is initially 
> 4MB in size.  This patch does not contain dynamic expansion, but that 
> could be added if necessary.
> 
> In our stress testing, our peak unecrypted DMA atomic allocation 
> requirements is ~1.4MB, so 4MB is plenty.  This pool is similar to the 
> existing DMA atomic pool but is unencrypted.
> 
> Signed-off-by: David Rientjes <rientjes@xxxxxxxxxx>
> ---
>  Based on v5.4 HEAD.
> 
>  This commit contains diagnostic information and is not intended for use 
>  in a production environment.
> 
>  arch/x86/Kconfig            |   1 +
>  drivers/iommu/dma-iommu.c   |   5 +-
>  include/linux/dma-mapping.h |   7 ++-
>  kernel/dma/direct.c         |  16 ++++-
>  kernel/dma/remap.c          | 116 ++++++++++++++++++++++++++----------
>  5 files changed, 108 insertions(+), 37 deletions(-)
> 
> diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
> --- a/arch/x86/Kconfig
> +++ b/arch/x86/Kconfig
> @@ -1530,6 +1530,7 @@ config X86_CPA_STATISTICS
>  config AMD_MEM_ENCRYPT
>  	bool "AMD Secure Memory Encryption (SME) support"
>  	depends on X86_64 && CPU_SUP_AMD
> +	select DMA_DIRECT_REMAP
>  	select DYNAMIC_PHYSICAL_MASK
>  	select ARCH_USE_MEMREMAP_PROT
>  	select ARCH_HAS_FORCE_DMA_UNENCRYPTED
> diff --git a/drivers/iommu/dma-iommu.c b/drivers/iommu/dma-iommu.c
> --- a/drivers/iommu/dma-iommu.c
> +++ b/drivers/iommu/dma-iommu.c
> @@ -928,7 +928,7 @@ static void __iommu_dma_free(struct device *dev, size_t size, void *cpu_addr)
>  
>  	/* Non-coherent atomic allocation? Easy */
>  	if (IS_ENABLED(CONFIG_DMA_DIRECT_REMAP) &&
> -	    dma_free_from_pool(cpu_addr, alloc_size))
> +	    dma_free_from_pool(dev, cpu_addr, alloc_size))
>  		return;
>  
>  	if (IS_ENABLED(CONFIG_DMA_REMAP) && is_vmalloc_addr(cpu_addr)) {
> @@ -1011,7 +1011,8 @@ static void *iommu_dma_alloc(struct device *dev, size_t size,
>  
>  	if (IS_ENABLED(CONFIG_DMA_DIRECT_REMAP) &&
>  	    !gfpflags_allow_blocking(gfp) && !coherent)
> -		cpu_addr = dma_alloc_from_pool(PAGE_ALIGN(size), &page, gfp);
> +		cpu_addr = dma_alloc_from_pool(dev, PAGE_ALIGN(size), &page,
> +					       gfp);
>  	else
>  		cpu_addr = iommu_dma_alloc_pages(dev, size, &page, gfp, attrs);
>  	if (!cpu_addr)
> diff --git a/include/linux/dma-mapping.h b/include/linux/dma-mapping.h
> --- a/include/linux/dma-mapping.h
> +++ b/include/linux/dma-mapping.h
> @@ -629,9 +629,10 @@ void *dma_common_pages_remap(struct page **pages, size_t size,
>  			pgprot_t prot, const void *caller);
>  void dma_common_free_remap(void *cpu_addr, size_t size);
>  
> -bool dma_in_atomic_pool(void *start, size_t size);
> -void *dma_alloc_from_pool(size_t size, struct page **ret_page, gfp_t flags);
> -bool dma_free_from_pool(void *start, size_t size);
> +bool dma_in_atomic_pool(struct device *dev, void *start, size_t size);
> +void *dma_alloc_from_pool(struct device *dev, size_t size,
> +			  struct page **ret_page, gfp_t flags);
> +bool dma_free_from_pool(struct device *dev, void *start, size_t size);
>  
>  int
>  dma_common_get_sgtable(struct device *dev, struct sg_table *sgt, void *cpu_addr,
> diff --git a/kernel/dma/direct.c b/kernel/dma/direct.c
> --- a/kernel/dma/direct.c
> +++ b/kernel/dma/direct.c
> @@ -10,6 +10,7 @@
>  #include <linux/dma-direct.h>
>  #include <linux/scatterlist.h>
>  #include <linux/dma-contiguous.h>
> +#include <linux/dma-mapping.h>
>  #include <linux/dma-noncoherent.h>
>  #include <linux/pfn.h>
>  #include <linux/set_memory.h>
> @@ -131,6 +132,13 @@ void *dma_direct_alloc_pages(struct device *dev, size_t size,
>  	struct page *page;
>  	void *ret;
>  
> +	if (!gfpflags_allow_blocking(gfp) && force_dma_unencrypted(dev)) {
> +		ret = dma_alloc_from_pool(dev, size, &page, gfp);
> +		if (!ret)
> +			return NULL;
> +		goto done;
> +	}
> +
>  	page = __dma_direct_alloc_pages(dev, size, dma_handle, gfp, attrs);
>  	if (!page)
>  		return NULL;
> @@ -156,7 +164,7 @@ void *dma_direct_alloc_pages(struct device *dev, size_t size,
>  		__dma_direct_free_pages(dev, size, page);
>  		return NULL;
>  	}
> -
> +done:
>  	ret = page_address(page);
>  	if (force_dma_unencrypted(dev)) {
>  		set_memory_decrypted((unsigned long)ret, 1 << get_order(size));
> @@ -185,6 +193,12 @@ void dma_direct_free_pages(struct device *dev, size_t size, void *cpu_addr,
>  {
>  	unsigned int page_order = get_order(size);
>  
> +	if (force_dma_unencrypted(dev) &&
> +	    dma_in_atomic_pool(dev, cpu_addr, size)) {
> +		dma_free_from_pool(dev, cpu_addr, size);
> +		return;
> +	}
> +
>  	if ((attrs & DMA_ATTR_NO_KERNEL_MAPPING) &&
>  	    !force_dma_unencrypted(dev)) {
>  		/* cpu_addr is a struct page cookie, not a kernel address */
> diff --git a/kernel/dma/remap.c b/kernel/dma/remap.c
> --- a/kernel/dma/remap.c
> +++ b/kernel/dma/remap.c
> @@ -8,6 +8,7 @@
>  #include <linux/dma-contiguous.h>
>  #include <linux/init.h>
>  #include <linux/genalloc.h>
> +#include <linux/set_memory.h>
>  #include <linux/slab.h>
>  #include <linux/vmalloc.h>
>  
> @@ -100,9 +101,11 @@ void dma_common_free_remap(void *cpu_addr, size_t size)
>  
>  #ifdef CONFIG_DMA_DIRECT_REMAP
>  static struct gen_pool *atomic_pool __ro_after_init;
> +static struct gen_pool *atomic_pool_unencrypted __ro_after_init;
>  
>  #define DEFAULT_DMA_COHERENT_POOL_SIZE  SZ_256K
>  static size_t atomic_pool_size __initdata = DEFAULT_DMA_COHERENT_POOL_SIZE;
> +static size_t atomic_pool_unencrypted_size __initdata = SZ_4M;
>  
>  static int __init early_coherent_pool(char *p)
>  {
> @@ -120,10 +123,11 @@ static gfp_t dma_atomic_pool_gfp(void)
>  	return GFP_KERNEL;
>  }
>  
> -static int __init dma_atomic_pool_init(void)
> +static int __init __dma_atomic_pool_init(struct gen_pool **pool,
> +				size_t pool_size, bool unencrypt)
>  {
> -	unsigned int pool_size_order = get_order(atomic_pool_size);
> -	unsigned long nr_pages = atomic_pool_size >> PAGE_SHIFT;
> +	unsigned int pool_size_order = get_order(pool_size);
> +	unsigned long nr_pages = pool_size >> PAGE_SHIFT;
>  	struct page *page;
>  	void *addr;
>  	int ret;
> @@ -136,78 +140,128 @@ static int __init dma_atomic_pool_init(void)
>  	if (!page)
>  		goto out;
>  
> -	arch_dma_prep_coherent(page, atomic_pool_size);
> +	arch_dma_prep_coherent(page, pool_size);
>  
> -	atomic_pool = gen_pool_create(PAGE_SHIFT, -1);
> -	if (!atomic_pool)
> +	*pool = gen_pool_create(PAGE_SHIFT, -1);
> +	if (!*pool)
>  		goto free_page;
>  
> -	addr = dma_common_contiguous_remap(page, atomic_pool_size,
> +	addr = dma_common_contiguous_remap(page, pool_size,
>  					   pgprot_dmacoherent(PAGE_KERNEL),
>  					   __builtin_return_address(0));
>  	if (!addr)
>  		goto destroy_genpool;
>  
> -	ret = gen_pool_add_virt(atomic_pool, (unsigned long)addr,
> -				page_to_phys(page), atomic_pool_size, -1);
> +	ret = gen_pool_add_virt(*pool, (unsigned long)addr, page_to_phys(page),
> +				pool_size, -1);
>  	if (ret)
>  		goto remove_mapping;
> -	gen_pool_set_algo(atomic_pool, gen_pool_first_fit_order_align, NULL);
> +	gen_pool_set_algo(*pool, gen_pool_first_fit_order_align, NULL);
> +	if (unencrypt)
> +		set_memory_decrypted((unsigned long)page_to_virt(page), nr_pages);
>  
> -	pr_info("DMA: preallocated %zu KiB pool for atomic allocations\n",
> -		atomic_pool_size / 1024);
> +	pr_info("DMA: preallocated %zu KiB pool for atomic allocations%s\n",
> +		pool_size >> 10, unencrypt ? " (unencrypted)" : "");
>  	return 0;
>  
>  remove_mapping:
> -	dma_common_free_remap(addr, atomic_pool_size);
> +	dma_common_free_remap(addr, pool_size);
>  destroy_genpool:
> -	gen_pool_destroy(atomic_pool);
> -	atomic_pool = NULL;
> +	gen_pool_destroy(*pool);
> +	*pool = NULL;
>  free_page:
>  	if (!dma_release_from_contiguous(NULL, page, nr_pages))
>  		__free_pages(page, pool_size_order);
>  out:
> -	pr_err("DMA: failed to allocate %zu KiB pool for atomic coherent allocation\n",
> -		atomic_pool_size / 1024);
> +	pr_err("DMA: failed to allocate %zu KiB pool for atomic coherent allocation%s\n",
> +		pool_size >> 10, unencrypt ? " (unencrypted)" : "");
>  	return -ENOMEM;
>  }
> +
> +static int __init dma_atomic_pool_init(void)
> +{
> +	int ret;
> +
> +	ret = __dma_atomic_pool_init(&atomic_pool, atomic_pool_size, false);
> +	if (ret)
> +		return ret;
> +	return __dma_atomic_pool_init(&atomic_pool_unencrypted,
> +				      atomic_pool_unencrypted_size, true);
> +}
>  postcore_initcall(dma_atomic_pool_init);
>  
> -bool dma_in_atomic_pool(void *start, size_t size)
> +static inline struct gen_pool *dev_to_pool(struct device *dev)
>  {
> -	if (unlikely(!atomic_pool))
> -		return false;
> +	if (force_dma_unencrypted(dev))
> +		return atomic_pool_unencrypted;
> +	return atomic_pool;
> +}
> +
> +bool dma_in_atomic_pool(struct device *dev, void *start, size_t size)
> +{
> +	struct gen_pool *pool = dev_to_pool(dev);
>  
> -	return addr_in_gen_pool(atomic_pool, (unsigned long)start, size);
> +	if (unlikely(!pool))
> +		return false;
> +	return addr_in_gen_pool(pool, (unsigned long)start, size);
>  }
>  
> -void *dma_alloc_from_pool(size_t size, struct page **ret_page, gfp_t flags)
> +static struct gen_pool *atomic_pool __ro_after_init;
> +static size_t encrypted_pool_size;
> +static size_t encrypted_pool_size_max;
> +static spinlock_t encrypted_pool_size_lock;
> +
> +void *dma_alloc_from_pool(struct device *dev, size_t size,
> +			  struct page **ret_page, gfp_t flags)
>  {
> +	struct gen_pool *pool = dev_to_pool(dev);
>  	unsigned long val;
>  	void *ptr = NULL;
>  
> -	if (!atomic_pool) {
> -		WARN(1, "coherent pool not initialised!\n");
> +	if (!pool) {
> +		WARN(1, "%scoherent pool not initialised!\n",
> +			force_dma_unencrypted(dev) ? "encrypted " : "");
>  		return NULL;
>  	}
>  
> -	val = gen_pool_alloc(atomic_pool, size);
> +	val = gen_pool_alloc(pool, size);
>  	if (val) {
> -		phys_addr_t phys = gen_pool_virt_to_phys(atomic_pool, val);
> +		phys_addr_t phys = gen_pool_virt_to_phys(pool, val);
>  
>  		*ret_page = pfn_to_page(__phys_to_pfn(phys));
>  		ptr = (void *)val;
>  		memset(ptr, 0, size);
> +		if (force_dma_unencrypted(dev)) {
> +			unsigned long flags;
> +
> +			spin_lock_irqsave(&encrypted_pool_size_lock, flags);
> +			encrypted_pool_size += size;
> +			if (encrypted_pool_size > encrypted_pool_size_max) {
> +				encrypted_pool_size_max = encrypted_pool_size;
> +				pr_info("max encrypted pool size now %lu\n",
> +					encrypted_pool_size_max);
> +			}
> +			spin_unlock_irqrestore(&encrypted_pool_size_lock, flags);
> +		}
>  	}
>  
>  	return ptr;
>  }
>  
> -bool dma_free_from_pool(void *start, size_t size)
> +bool dma_free_from_pool(struct device *dev, void *start, size_t size)
>  {
> -	if (!dma_in_atomic_pool(start, size))
> +	struct gen_pool *pool = dev_to_pool(dev);
> +
> +	if (!dma_in_atomic_pool(dev, start, size))
>  		return false;
> -	gen_pool_free(atomic_pool, (unsigned long)start, size);
> +	gen_pool_free(pool, (unsigned long)start, size);
> +	if (force_dma_unencrypted(dev)) {
> +		unsigned long flags;
> +
> +		spin_lock_irqsave(&encrypted_pool_size_lock, flags);
> +		encrypted_pool_size -= size;
> +		spin_unlock_irqrestore(&encrypted_pool_size_lock, flags);
> +	}
>  	return true;
>  }
>  
> @@ -220,7 +274,7 @@ void *arch_dma_alloc(struct device *dev, size_t size, dma_addr_t *dma_handle,
>  	size = PAGE_ALIGN(size);
>  
>  	if (!gfpflags_allow_blocking(flags)) {
> -		ret = dma_alloc_from_pool(size, &page, flags);
> +		ret = dma_alloc_from_pool(dev, size, &page, flags);
>  		if (!ret)
>  			return NULL;
>  		goto done;
> @@ -251,7 +305,7 @@ void *arch_dma_alloc(struct device *dev, size_t size, dma_addr_t *dma_handle,
>  void arch_dma_free(struct device *dev, size_t size, void *vaddr,
>  		dma_addr_t dma_handle, unsigned long attrs)
>  {
> -	if (!dma_free_from_pool(vaddr, PAGE_ALIGN(size))) {
> +	if (!dma_free_from_pool(dev, vaddr, PAGE_ALIGN(size))) {
>  		phys_addr_t phys = dma_to_phys(dev, dma_handle);
>  		struct page *page = pfn_to_page(__phys_to_pfn(phys));
>  
>