VM66254: USER HANG DUE TO LOST PAGING READ/WRITE

Obtain the fix for this APAR.

APAR status

• Closed as program error.

Error description

• A z/VM guest can appear to be hung either during normal guest
  execution or at logoff.
  
  A request to page in or out a guest page can be lost due to
  incorrect paging request queue management.
  

Local fix

• N/A
  

Problem summary

• ****************************************************************
  * USERS AFFECTED: All users of z/VM systems with more than 512 *
  *                 GB of real storage/memory.                   *
  ****************************************************************
  * PROBLEM DESCRIPTION:                                         *
  ****************************************************************
  * RECOMMENDATION: APPLY PTF                                    *
  ****************************************************************
  Guest hangs can occur due to lost paging requests to read or
  write a guest page.  This can cause a guest to hang during
  normal execution or logoff.
  
  In the paging code, there is incorrect queue management
  logic.  The code loads a 64-bit value, but then uses a
  32-bit test for zero.  As such, if the low-order 32 bits of
  the address are zero, but high-order bits are non-zero, the
  test will take the wrong branch.  This will result in
  overwriting the queue anchors, instead of appending to the
  queue, and losing the FRMTEs that were already in the queue.
  In the specific area of code, the 64-bit address is a FRMTE
  address.  Owing to the way the frame table is organized, FRMTEs
  with a zero low half, and non-zero high half represent the
  frames at 512 GB, 1 TB, and 1.5 TB.  So if one of these
  specific FRMTEs happens to be at the front of a read or write
  queue, the read/write request for this frame and any that
  happen to be after it will be lost.
  
  Only systems with greater than 512 GB of real memory are
  affected by this problem.
  

Problem conclusion

• Code in module HCPPAI is corrected to do a 64-bit check
  for zero on the queue anchors.
  

Temporary fix

Comments

APAR Information

• APAR is sysrouted FROM one or more of the following:

• APAR is sysrouted TO one or more of the following:

  UM35434 UM35435

Modules/Macros

• HCPPAI
  

Fix information

• Fixed component name

  VM CP

• Fixed component ID

  568411202

Applicable component levels

• R640 PSY UM35434

     UP19/03/06 P 2001 ¢

• R710 PSY UM35435

     UP19/09/26 P 1902 ¢

Fix is available

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