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Date: Tue, 14 Apr 2020 12:18:37 -0700 (PDT)
From: David Rientjes <rientjes@...gle.com>
To: Tom Lendacky <thomas.lendacky@....com>
cc: Christoph Hellwig <hch@....de>,
"Singh, Brijesh" <brijesh.singh@....com>,
"Grimm, Jon" <jon.grimm@....com>, Joerg Roedel <joro@...tes.org>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
"iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>
Subject: Re: [rfc v2 4/6] dma-direct: atomic allocations must come from atomic
coherent pools
On Thu, 9 Apr 2020, Tom Lendacky wrote:
> > When a device required unencrypted memory and the context does not allow
>
> required => requires
>
Fixed, thanks.
> > blocking, memory must be returned from the atomic coherent pools.
> >
> > This avoids the remap when CONFIG_DMA_DIRECT_REMAP is not enabled and the
> > config only requires CONFIG_DMA_COHERENT_POOL. This will be used for
> > CONFIG_AMD_MEM_ENCRYPT in a subsequent patch.
> >
> > Keep all memory in these pools unencrypted.
> >
> > Signed-off-by: David Rientjes <rientjes@...gle.com>
> > ---
> > kernel/dma/direct.c | 16 ++++++++++++++++
> > kernel/dma/pool.c | 15 +++++++++++++--
> > 2 files changed, 29 insertions(+), 2 deletions(-)
> >
> > diff --git a/kernel/dma/direct.c b/kernel/dma/direct.c
> > index 70800ca64f13..44165263c185 100644
> > --- a/kernel/dma/direct.c
> > +++ b/kernel/dma/direct.c
> > @@ -124,6 +124,18 @@ void *dma_direct_alloc_pages(struct device *dev, size_t
> > size,
> > struct page *page;
> > void *ret;
> > + /*
> > + * Unencrypted memory must come directly from DMA atomic pools if
> > + * blocking is not allowed.
> > + */
> > + if (IS_ENABLED(CONFIG_DMA_COHERENT_POOL) &&
> > + force_dma_unencrypted(dev) && !gfpflags_allow_blocking(gfp)) {
> > + ret = dma_alloc_from_pool(dev, PAGE_ALIGN(size), &page, gfp);
> > + if (!ret)
> > + return NULL;
> > + goto done;
> > + }
> > +
> > if (IS_ENABLED(CONFIG_DMA_DIRECT_REMAP) &&
> > dma_alloc_need_uncached(dev, attrs) &&
> > !gfpflags_allow_blocking(gfp)) {
> > @@ -203,6 +215,10 @@ void dma_direct_free_pages(struct device *dev, size_t
> > size, void *cpu_addr,
> > {
> > unsigned int page_order = get_order(size);
> > + if (IS_ENABLED(CONFIG_DMA_COHERENT_POOL) &&
> > + dma_free_from_pool(dev, cpu_addr, PAGE_ALIGN(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/pool.c b/kernel/dma/pool.c
> > index e14c5a2da734..6685ab89cfa7 100644
> > --- a/kernel/dma/pool.c
> > +++ b/kernel/dma/pool.c
> > @@ -9,6 +9,7 @@
> > #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>
> > #include <linux/workqueue.h>
> > @@ -55,12 +56,20 @@ static int atomic_pool_expand(struct gen_pool *pool,
> > size_t pool_size,
> > arch_dma_prep_coherent(page, pool_size);
> > +#ifdef CONFIG_DMA_DIRECT_REMAP
> > addr = dma_common_contiguous_remap(page, pool_size,
> > pgprot_dmacoherent(PAGE_KERNEL),
> > __builtin_return_address(0));
> > if (!addr)
> > goto free_page;
> > -
> > +#else
> > + addr = page_to_virt(page);
> > +#endif
> > + /*
> > + * Memory in the atomic DMA pools must be unencrypted, the pools do
> > not
> > + * shrink so no re-encryption occurs in dma_direct_free_pages().
> > + */
> > + set_memory_decrypted((unsigned long)page_to_virt(page), 1 << order);
> > ret = gen_pool_add_virt(pool, (unsigned long)addr, page_to_phys(page),
> > pool_size, NUMA_NO_NODE);
> > if (ret)
> > @@ -69,8 +78,10 @@ static int atomic_pool_expand(struct gen_pool *pool,
> > size_t pool_size,
> > return 0;
> > remove_mapping:
> > +#ifdef CONFIG_DMA_DIRECT_REMAP
> > dma_common_free_remap(addr, pool_size);
>
> You're about to free the memory, but you've called set_memory_decrypted()
> against it, so you need to do a set_memory_encrypted() to bring it back to a
> state ready for allocation again.
>
Ah, good catch, thanks. I notice that I should also be checking the
return value of set_memory_decrypted() because pages added to the coherent
pools *must* be unencrypted. If it fails, we fail the expansion.
And do the same thing for set_memory_encrypted(), which would be a bizarre
situation (decrypt succeeded, encrypt failed), by simply leaking the page.
diff --git a/kernel/dma/pool.c b/kernel/dma/pool.c
--- a/kernel/dma/pool.c
+++ b/kernel/dma/pool.c
@@ -7,6 +7,7 @@
#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>
#include <linux/workqueue.h>
@@ -53,22 +54,42 @@ static int atomic_pool_expand(struct gen_pool *pool, size_t pool_size,
arch_dma_prep_coherent(page, pool_size);
+#ifdef CONFIG_DMA_DIRECT_REMAP
addr = dma_common_contiguous_remap(page, pool_size,
pgprot_dmacoherent(PAGE_KERNEL),
__builtin_return_address(0));
if (!addr)
goto free_page;
-
+#else
+ addr = page_to_virt(page);
+#endif
+ /*
+ * Memory in the atomic DMA pools must be unencrypted, the pools do not
+ * shrink so no re-encryption occurs in dma_direct_free_pages().
+ */
+ ret = set_memory_decrypted((unsigned long)page_to_virt(page),
+ 1 << order);
+ if (ret)
+ goto remove_mapping;
ret = gen_pool_add_virt(pool, (unsigned long)addr, page_to_phys(page),
pool_size, NUMA_NO_NODE);
if (ret)
- goto remove_mapping;
+ goto encrypt_mapping;
return 0;
+encrypt_mapping:
+ ret = set_memory_encrypted((unsigned long)page_to_virt(page),
+ 1 << order);
+ if (WARN_ON_ONCE(ret)) {
+ /* Decrypt succeeded but encrypt failed, purposely leak */
+ goto out;
+ }
remove_mapping:
+#ifdef CONFIG_DMA_DIRECT_REMAP
dma_common_free_remap(addr, pool_size);
-free_page:
+#endif
+free_page: __maybe_unused
if (!dma_release_from_contiguous(NULL, page, 1 << order))
__free_pages(page, order);
out:
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