Re: [PATCH 3/4] s390/mm: prevent and break zero page mappings in case of storage keys

[Paolo Bonzini]

On 10/22/2014 10:30 AM, Dominik Dingel wrote:
> As use_skey is already the condition on which we call s390_enable_skey
> we need to introduce a new flag for the mm->context on which we decide
> if zero page mapping is allowed.

Can you explain better why "mm->context.use_skey = 1" cannot be done
before the walk_page_range?  Where does the walk or __s390_enable_skey
or (after the next patch) ksm_madvise rely on
"mm->context.forbids_zeropage && !mm->context.use_skey"?

The only reason I can think of, is that the next patch does not reset
"mm->context.forbids_zeropage" to 0 if the ksm_madvise fails.  Why
doesn't it do that---or is it a bug?

Thanks, and sorry for the flurry of questions! :)

Paolo
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