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Re: [Qemu-devel] [RFC PATCH 1/2] e1000: Use Address_Available bit as HW
From: |
Vlad Yasevich |
Subject: |
Re: [Qemu-devel] [RFC PATCH 1/2] e1000: Use Address_Available bit as HW latch |
Date: |
Fri, 22 Nov 2013 09:37:58 -0500 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:24.0) Gecko/20100101 Thunderbird/24.1.0 |
On 11/22/2013 04:47 AM, Jason Wang wrote:
> On 11/22/2013 04:04 AM, Vlad Yasevich wrote:
>> e1000 provides a E1000_RAH_AV bit on every complete write
>> to the Receive Address Register. We can use this bit
>> 2 ways:
>> 1) To trigger HMP notifications. When the bit is set the
>> mac address is fully set and we can update the HMP.
>>
>> 2) We can turn off he bit on the write to low order bits of
>> the Receive Address Register, so that we would not try
>> to match received traffic to this address when it is
>> not completely set.
>>
>> Signed-off-by: Vlad Yasevich <address@hidden>
>> ---
>> hw/net/e1000.c | 11 ++++++++++-
>> 1 file changed, 10 insertions(+), 1 deletion(-)
>>
>> diff --git a/hw/net/e1000.c b/hw/net/e1000.c
>> index ae63591..82978ea 100644
>> --- a/hw/net/e1000.c
>> +++ b/hw/net/e1000.c
>> @@ -1106,10 +1106,19 @@ mac_writereg(E1000State *s, int index, uint32_t val)
>>
>> s->mac_reg[index] = val;
>>
>> - if (index == RA || index == RA + 1) {
>> + switch (index) {
>> + case RA:
>> + /* Mask off AV bit on the write of the low dword. The write of
>> + * the high dword will set the bit. This way a half-written
>> + * mac address will not be used to filter on rx.
>> + */
>> + s->mac_reg[RA+1] &= ~E1000_RAH_AV;
>
> If a stupid driver write high dword first, it won't receive any packets.
I need to ping Intel guys again. I asked them what happens when only
the low register is set, but haven't heard back.
>> + break;
>> + case (RA + 1):
>> macaddr[0] = cpu_to_le32(s->mac_reg[RA]);
>> macaddr[1] = cpu_to_le32(s->mac_reg[RA + 1]);
>> qemu_format_nic_info_str(qemu_get_queue(s->nic), (uint8_t
>> *)macaddr);
>
> Guest may invalid the mac address by clearing the AV bit through writing
> to high dword. So this may notify a wrong mac address.
In this case, testing for the AV bit would solve this issue.
>
> Generally, we could teset the AV bit before notification, and try to do
> the this on both high and low dword. This obeys specs and
> receive_filter() above.
This will not really help since the AV bit would already be set from the
prior mac address. So, if a stupid driver writes just the low word,
the AV bit would already be set.
>
> If we don't want half-written status, driver should clear AV bit before
> each writing of new mac address. But looks like linux and freebsd does
> not do this. But the window is really small and harmless.
We can emulate this. Thanks for the idea.
-vlad
>> + break;
>> }
>> }
>>
>