sfc: Restrict PIO for 64bit arch in order to avoid data corruption

PATCH Superseded Shradha Shah 2 participants 4 messages May 28, 2014 – May 31, 2014

Subsystems (3)

Networking Network drivers Sfc network driver

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Shradha Shah

author

2014-05-28 09:23 UTC #0 lore raw

v2 cover sfc: Restrict PIO for 64bit arch in order to avoid data corruption

This patch series

Fixes ee45fd92c739db5b7950163d91dfe5f016af6d24

The linux net driver uses memcpy_toio() in order to copy into the PIO buffers.
Even on a 64bit machine this causes 32bit accesses to a write- combined memory region.
There are hardware limitations that mean that only
64bit naturally aligned accesses are safe in all cases. Due to being write-combined memory region two 32bit accesses may be coalesced to form a 64bit non 64bit aligned access.
Solution was to open-code the memory copy routines using pointers and to only enable PIO for x86_64 machines.

This bug fix applies to v3.13 and v3.14 stable branches.

Jon Cooper (2):
sfc: use 64-bit writes for PIO.
sfc: Restrict PIO to 64-bit architectures

 drivers/net/ethernet/sfc/io.h |  8 ++++++++
 drivers/net/ethernet/sfc/tx.c | 24 +++++++++++++++++++-----
 2 files changed, 27 insertions(+), 5 deletions(-)

Shradha Shah

author

2014-05-28 09:28 UTC #1 lore raw

PATCH v2 1/2 sfc: use 64-bit writes for PIO.

From: Jon Cooper <[email protected]>

Patch to open-code the memory copy routines. 32bit writes over the PCI bus causes data corruption.

Fixes ee45fd92c739db5b7950163d91dfe5f016af6d24

orig-hg-hash: 853f313def1e5e9c733f980f2b4e6330a7d063ef

Signed-off-by Shradha Shah <[email protected]>

---
 drivers/net/ethernet/sfc/tx.c | 24 +++++++++++++++++++-----
 1 file changed, 19 insertions(+), 5 deletions(-)

drivers/net/ethernet/sfc/tx.c +19 -5

index fa94753..bd6a4b8 100644
@@ -189,6 +189,20 @@ struct efx_short_copy_buffer {
 	u8 buf[L1_CACHE_BYTES];
 };
 
+/* Copy in explicit 64-bit writes. */
+static void efx_memcpy_64(void *dest, void *src, size_t len)
+{
+	uint64_t *src64 = src, *dest64 = dest;
+	size_t i, l64 = len / 8;
+
+	WARN_ON_ONCE(len % 8 != 0);
+	WARN_ON_ONCE(((u8 *)dest - (u8 *) 0) % 8 != 0);
+	BUILD_BUG_ON(sizeof(uint64_t) != 8);
+
+	for(i = 0; i < l64; ++i)
+		dest64[i] = src64[i];
+}
+
 /* Copy to PIO, respecting that writes to PIO buffers must be dword aligned.
  * Advances piobuf pointer. Leaves additional data in the copy buffer.
  */

@@ -198,7 +212,7 @@ static void efx_memcpy_toio_aligned(struct efx_nic *efx, u8 __iomem **piobuf,
 {
 	int block_len = len & ~(sizeof(copy_buf->buf) - 1);
 
-	memcpy_toio(*piobuf, data, block_len);
+	efx_memcpy_64(*piobuf, data, block_len);
 	*piobuf += block_len;
 	len -= block_len;

@@ -230,7 +244,7 @@ static void efx_memcpy_toio_aligned_cb(struct efx_nic *efx, u8 __iomem **piobuf,
 		if (copy_buf->used < sizeof(copy_buf->buf))
 			return;
 
-		memcpy_toio(*piobuf, copy_buf->buf, sizeof(copy_buf->buf));
+		efx_memcpy_64(*piobuf, copy_buf->buf, sizeof(copy_buf->buf));
 		*piobuf += sizeof(copy_buf->buf);
 		data += copy_to_buf;
 		len -= copy_to_buf;

@@ -245,7 +259,7 @@ static void efx_flush_copy_buffer(struct efx_nic *efx, u8 __iomem *piobuf,
 {
 	/* if there's anything in it, write the whole buffer, including junk */
 	if (copy_buf->used)
-		memcpy_toio(piobuf, copy_buf->buf, sizeof(copy_buf->buf));
+		efx_memcpy_64(piobuf, copy_buf->buf, sizeof(copy_buf->buf));
 }
 
 /* Traverse skb structure and copy fragments in to PIO buffer.

@@ -304,8 +318,8 @@ efx_enqueue_skb_pio(struct efx_tx_queue *tx_queue, struct sk_buff *skb)
 		 */
 		BUILD_BUG_ON(L1_CACHE_BYTES >
 			     SKB_DATA_ALIGN(sizeof(struct skb_shared_info)));
-		memcpy_toio(tx_queue->piobuf, skb->data,
-			    ALIGN(skb->len, L1_CACHE_BYTES));
+		efx_memcpy_64(tx_queue->piobuf, skb->data,
+			      ALIGN(skb->len, L1_CACHE_BYTES));
 	}
 
 	EFX_POPULATE_QWORD_5(buffer->option,

Shradha Shah

author

2014-05-28 09:30 UTC #2 lore raw

PATCH v2 2/2 sfc: Restrict PIO to 64-bit architectures

In reply to Shradha Shah

From: Jon Cooper <[email protected]>

Enable PIO for x86_64 architecture only.
Not tested on platforms other than x86_64.

Fixes ee45fd92c739db5b7950163d91dfe5f016af6d24

orig-hg-hash: 53dc43553d9bbe1c5a64c49e580ca571ddc470ae

Signed-off-by Shradha Shah <[email protected]>

---
 drivers/net/ethernet/sfc/io.h | 8 ++++++++
 1 file changed, 8 insertions(+)

drivers/net/ethernet/sfc/io.h +8 -0

index 4d3f119..adadcf0 100644
@@ -66,10 +66,18 @@
 #define EFX_USE_QWORD_IO 1
 #endif
 
+/* PIO only works on 64-bit architectures */
+#if BITS_PER_LONG == 64
+/* not strictly necessary to restrict to x86 arch, but done for safety
+ * since unusual write combining behaviour can break PIO.
+ */
+#ifdef CONFIG_X86_64
 /* PIO is a win only if write-combining is possible */
 #ifdef ARCH_HAS_IOREMAP_WC
 #define EFX_USE_PIO 1
 #endif
+#endif
+#endif
 
 #ifdef EFX_USE_QWORD_IO
 static inline void _efx_writeq(struct efx_nic *efx, __le64 value,

David Miller

maintainer

2014-05-31 00:38 UTC #3 lore raw

In reply to Shradha Shah

From: Shradha Shah <[email protected]>
Date: Wed, 28 May 2014 10:23:01 +0100

Quoted 14 lines

This patch series
Fixes ee45fd92c739db5b7950163d91dfe5f016af6d24
The linux net driver uses memcpy_toio() in order to copy into the PIO buffers.
Even on a 64bit machine this causes 32bit accesses to a write- combined memory region.
There are hardware limitations that mean that only
64bit naturally aligned accesses are safe in all cases. Due to being write-combined memory region two 32bit accesses may be coalesced to form a 64bit non 64bit aligned access.
Solution was to open-code the memory copy routines using pointers and to only enable PIO for x86_64 machines.

Quoted 1 line

This bug fix applies to v3.13 and v3.14 stable branches.

You submited this twice and I'm still confused which ones I should use.

Please resubmit this and address Sergei's feedback, thank you.