netdev - Re: [PATCH] bpf: fix size of copy_to

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Date:   Thu, 18 Aug 2016 18:38:20 -0700
From:   William Tu <u9012063@...il.com>
To:     Alexei Starovoitov <alexei.starovoitov@...il.com>
Cc:     Daniel Borkmann <daniel@...earbox.net>,
        Linux Kernel Network Developers <netdev@...r.kernel.org>
Subject: Re: [PATCH] bpf: fix size of copy_to_user in percpu map.

Hi Alexei and Daniel,

I got feedback from Fusion bios/chipset team. In short, the value
'possible' includes empty CPU socket. To verify, I tested on a
physical Xeon machine with 2 CPU sockets, one of them is empty. I got
'possible' = 0-239, the number of 'cpu*' =12. As a result, extra bytes
are copied from kernel to userspace.

As for Fusion, there is a configuration in *.vmx. If we disable cpu
hot plug by "vcpu.hotadd=FALSE", then 'possible' ==  the number of
'cpu*' dirs, which is the configuration in ESX. If "vcpu.hotadd=TURE",
then 'possible' is larger than 'cpu*' dirs, allowing users to add more
vcpus.

Regards,
William

On Fri, Aug 12, 2016 at 4:08 PM, Alexei Starovoitov
<alexei.starovoitov@...il.com> wrote:
> On Fri, Aug 12, 2016 at 09:58:51AM -0700, William Tu wrote:
>> Hi,
>>
>> I've tested on ESXi version 5.5 and it seems OK.
>> - VM1: Ubuntu 14.04, kernel 3.19 ---> OK 3 cpu dirs, possible = 0-2
>> - VM2: Centos7, kernel 3.10 ---> OK 8 cpu dirs, possible = 0-7
>>
>> I tried another MacBook with Fusion, same issue happens, the cpu[0-9]
>> dirs are not equal to /sys/devices/system/cpu/possible
>
> great. thanks for testing. I think the issue is closed and
> hopefully you can follow up with fusion guys ;)
>