KVM: s390: pv: avoid stalls when making pages secure

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Improve make_secure_pte to avoid stalls when the system is heavily
overcommitted. This was especially problematic in kvm_s390_pv_unpack,
because of the loop over all pages that needed unpacking.

Due to the locks being held, it was not possible to simply replace
uv_call with uv_call_sched. A more complex approach was
needed, in which uv_call is replaced with __uv_call, which does not
loop. When the UVC needs to be executed again, -EAGAIN is returned, and
the caller (or its caller) will try again.

When -EAGAIN is returned, the path is the same as when the page is in
writeback (and the writeback check is also performed, which is
harmless).

Fixes: 214d9bbcd3 ("s390/mm: provide memory management functions for protected KVM guests")
Signed-off-by: Claudio Imbrenda <imbrenda@linux.ibm.com>
Reviewed-by: Janosch Frank <frankja@linux.ibm.com>
Reviewed-by: Christian Borntraeger <borntraeger@de.ibm.com>
Link: https://lore.kernel.org/r/20210920132502.36111-5-imbrenda@linux.ibm.com
Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>

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Claudio Imbrenda 2021-09-20 15:24:52 +02:00 • committed by Christian Borntraeger

parent 1e2aa46de5

commit f0a1a0615a

2 changed files with 28 additions and 6 deletions

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29

arch/s390/kernel/uv.c

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5

arch/s390/kvm/intercept.c

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