Subject: Re: [PATCH kernel 5/9] KVM: PPC: Account TCE-containing pages in locked_vm

From: Alexey Kardashevskiy <[email-masked]>
Date: Mon, 30 Nov 2015 16:09:27 +1100

On 11/30/2015 01:06 PM, Paul Mackerras wrote:
> On Tue, Sep 15, 2015 at 08:49:35PM +1000, Alexey Kardashevskiy wrote:
>> At the moment pages used for TCE tables (in addition to pages addressed
>> by TCEs) are not counted in locked_vm counter so a malicious userspace
>> tool can call ioctl(KVM_CREATE_SPAPR_TCE) as many times as RLIMIT_NOFILE and
>> lock a lot of memory.
>>
>> This adds counting for pages used for TCE tables.
>>
>> This counts the number of pages required for a table plus pages for
>> the kvmppc_spapr_tce_table struct (TCE table descriptor) itself.
>>
>> This does not change the amount of (de)allocated memory.
>>
>> Signed-off-by: Alexey Kardashevskiy <[email-masked]>
>> ---
>>   arch/powerpc/kvm/book3s_64_vio.c | 51 +++++++++++++++++++++++++++++++++++++++-
>>   1 file changed, 50 insertions(+), 1 deletion(-)
>>
>> diff --git a/arch/powerpc/kvm/book3s_64_vio.c b/arch/powerpc/kvm/book3s_64_vio.c
>> index 9526c34..b70787d 100644
>> --- a/arch/powerpc/kvm/book3s_64_vio.c
>> +++ b/arch/powerpc/kvm/book3s_64_vio.c
>> @@ -45,13 +45,56 @@ static long kvmppc_stt_npages(unsigned long window_size)
>>   		     * sizeof(u64), PAGE_SIZE) / PAGE_SIZE;
>>   }
>>
>> +static long kvmppc_account_memlimit(long npages, bool inc)
>> +{
>> +	long ret = 0;
>> +	const long bytes = sizeof(struct kvmppc_spapr_tce_table) +
>> +			(abs(npages) * sizeof(struct page *));
>
> Why abs(npages)?  Can npages be negative?  If so, what does that mean?

Leftover from older versions when there was one shared 
account_memlimit(long npages). It does not make sense here, I need to 
remove it.

-- 
Alexey