path: root/drivers/net/ethernet
diff options
authorDean Nelson <dnelson@redhat.com>2011-09-16 16:52:54 +0000
committerJeff Kirsher <jeffrey.t.kirsher@intel.com>2011-09-28 23:06:57 -0700
commitd5bc77a223b0e9b9dfb002048d2b34a79e7d0b48 (patch)
tree98ad2cfbe1bb1244a02086f012b2c7c35e8e8086 /drivers/net/ethernet
parent2e1143742789463c00ed5e7f9bf471f2b707b493 (diff)
e1000: don't enable dma receives until after dma address has been setup
Doing an 'ifconfig ethN down' followed by an 'ifconfig ethN up' on a qemu-kvm guest system configured with two e1000 NICs can result in an 'unable to handle kernel paging request at 0000000100000000' or 'bad page map in process ...' or something similar. These result from a 4096-byte page being corrupted with the following two-word pattern (16-bytes) repeated throughout the entire page: 0x0000000000000000 0x0000000100000000 There can be other bits set as well. What is a constant is that the 2nd word has the 32nd bit set. So one could see: : 0x0000000000000000 0x0000000100000000 0x0000000000000000 0x0000000172adc067 <<< bad pte 0x800000006ec60067 0x0000000700000040 0x0000000000000000 0x0000000100000000 : Which came from from a process' page table I dumped out when the marked line was seen as bad by print_bad_pte(). The repeating pattern represents the e1000's two-word receive descriptor: struct e1000_rx_desc { __le64 buffer_addr; /* Address of the descriptor's data buffer */ __le16 length; /* Length of data DMAed into data buffer */ __le16 csum; /* Packet checksum */ u8 status; /* Descriptor status */ u8 errors; /* Descriptor Errors */ __le16 special; }; And the 32nd bit of the 2nd word maps to the 'u8 status' member, and corresponds to E1000_RXD_STAT_DD which indicates the descriptor is done. The corruption appears to result from the following... . An 'ifconfig ethN down' gets us into e1000_close(), which through a number of subfunctions results in: 1. E1000_RCTL_EN being cleared in RCTL register. [e1000_down()] 2. dma_free_coherent() being called. [e1000_free_rx_resources()] . An 'ifconfig ethN up' gets us into e1000_open(), which through a number of subfunctions results in: 1. dma_alloc_coherent() being called. [e1000_setup_rx_resources()] 2. E1000_RCTL_EN being set in RCTL register. [e1000_setup_rctl()] 3. E1000_RCTL_EN being cleared in RCTL register. [e1000_configure_rx()] 4. RDLEN, RDBAH and RDBAL registers being set to reflect the dma page allocated in step 1. [e1000_configure_rx()] 5. E1000_RCTL_EN being set in RCTL register. [e1000_configure_rx()] During the 'ifconfig ethN up' there is a window opened, starting in step 2 where the receives are enabled up until they are disabled in step 3, in which the address of the receive descriptor dma page known by the NIC is still the previous one which was freed during the 'ifconfig ethN down'. If this memory has been reallocated for some other use and the NIC feels so inclined, it will write to that former dma page with predictably unpleasant results. I realize that in the guest, we're dealing with an e1000 NIC that is software emulated by qemu-kvm. The problem doesn't appear to occur on bare-metal. Andy suspects that this is because in the emulator link-up is essentially instant and traffic can start flowing immediately. Whereas on bare-metal, link-up usually seems to take at least a few milliseconds. And this might be enough to prevent traffic from flowing into the device inside the window where E1000_RCTL_EN is set. So perhaps a modification needs to be made to the qemu-kvm e1000 NIC emulator to delay the link-up. But in defense of the emulator, it seems like a bad idea to enable dma operations before the address of the memory to be involved has been made known. The following patch no longer enables receives in e1000_setup_rctl() but leaves them however they were. It only enables receives in e1000_configure_rx(), and only after the dma address has been made known to the hardware. There are two places where e1000_setup_rctl() gets called. The one in e1000_configure() is followed immediately by a call to e1000_configure_rx(), so there's really no change functionally (except for the removal of the problem window. The other is in __e1000_shutdown() and is not followed by a call to e1000_configure_rx(), so there is a change functionally. But consider... . An 'ifconfig ethN down' (just as described above). . A 'suspend' of the system, which (I'm assuming) will find its way into e1000_suspend() which calls __e1000_shutdown() resulting in: 1. E1000_RCTL_EN being set in RCTL register. [e1000_setup_rctl()] And again we've re-opened the problem window for some unknown amount of time. Signed-off-by: Andy Gospodarek <andy@greyhouse.net> Signed-off-by: Dean Nelson <dnelson@redhat.com> Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
Diffstat (limited to 'drivers/net/ethernet')
1 files changed, 3 insertions, 3 deletions
diff --git a/drivers/net/ethernet/intel/e1000/e1000_main.c b/drivers/net/ethernet/intel/e1000/e1000_main.c
index 27f586afcc34..4bbc05ad9ba1 100644
--- a/drivers/net/ethernet/intel/e1000/e1000_main.c
+++ b/drivers/net/ethernet/intel/e1000/e1000_main.c
@@ -1814,8 +1814,8 @@ static void e1000_setup_rctl(struct e1000_adapter *adapter)
rctl &= ~(3 << E1000_RCTL_MO_SHIFT);
- rctl |= E1000_RCTL_EN | E1000_RCTL_BAM |
+ rctl |= E1000_RCTL_BAM | E1000_RCTL_LBM_NO |
(hw->mc_filter_type << E1000_RCTL_MO_SHIFT);
if (hw->tbi_compatibility_on == 1)
@@ -1917,7 +1917,7 @@ static void e1000_configure_rx(struct e1000_adapter *adapter)
/* Enable Receives */
- ew32(RCTL, rctl);
+ ew32(RCTL, rctl | E1000_RCTL_EN);