On 02/07/2018 12:38 AM, ebiederm@xxxxxxxxxxxx wrote:
Khalid Aziz <khalid.aziz@xxxxxxxxxx> writes:
On 02/01/2018 07:29 PM, ebiederm@xxxxxxxxxxxx wrote:
Khalid Aziz <khalid.aziz@xxxxxxxxxx> writes:
V11 changes:
This series is same as v10 and was simply rebased on 4.15 kernel. Can
mm maintainers please review patches 2, 7, 8 and 9 which are arch
independent, and include/linux/mm.h and mm/ksm.c changes in patch 10
and ack these if everything looks good?
I am a bit puzzled how this differs from the pkey's that other
architectures are implementing to achieve a similar result.
I am a bit mystified why you don't store the tag in a vma
instead of inventing a new way to store data on page out.
Hello Eric,
As Steven pointed out, sparc sets tags per cacheline unlike pkey. This results
in much finer granularity for tags that pkey and hence requires larger tag
storage than what we can do in a vma.
*Nod* I am a bit mystified where you keep the information in memory.
I would think the tags would need to be stored per cacheline or per
tlb entry, in some kind of cache that could overflow. So I would be
surprised if swapping is the only time this information needs stored
in memory. Which makes me wonder if you have the proper data
structures.
I would think an array per vma or something in the page tables would
tend to make sense.
But perhaps I am missing something.
The ADI tags are stored in spare bits in the RAM. ADI tag storage is
managed entirely by memory controller which maintains these tags per ADI
block. An ADI block is the same size as cacheline on M7. Tags for each
ADI block are associated with the physical ADI block, not the virtual
address. When a physical page is reused, the physical ADI tag storage
for that page is overwritten with new ADI tags, hence we need to store
away the tags when we swap out a page. Kernel updates the ADI tags for
physical page when it swaps a new page in. Each vma can cover variable
number of pages so it is best to store a pointer to the tag storage in
vma as opposed to actual tags in an array. Each 8K page can have 128
tags on it. Since each tag is 4 bits, we need 64 bytes per page to store
the tags. That can add up for a large vma.
Can you please use force_sig_fault to send these signals instead
of force_sig_info. Emperically I have found that it is very
error prone to generate siginfo's by hand, especially on code
paths where several different si_codes may apply. So it helps
to go through a helper function to ensure the fiddly bits are
all correct. AKA the unused bits all need to be set to zero before
struct siginfo is copied to userspace.
What you say makes sense. I followed the same code as other fault handlers for
sparc. I could change just the fault handlers for ADI related faults. Would it
make more sense to change all the fault handlers in a separate patch and keep
the code in arch/sparc/kernel/traps_64.c consistent? Dave M, do you have a
preference?
It is my intention post -rc1 to start sending out patches to get the
rest of not just sparc but all of the architectures using the new
helpers. I have the code I just ran out of time befor the merge
window opened to ensure everything had a good thorough review.
So if you can handle the your new changes I expect I will handle the
rest.
I can add a patch at the end of my series to update all force_sig_info()
in my patchset to force_sig_fault(). That will sync my patches up with
your changes cleanly. Does that work for you? I can send an updated
series with this change. Can you review and ack the patches after this
change.
Thanks,
Khalid
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