A fix is available
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 number
VM66254
Reported component name
VM CP
Reported component ID
568411202
Reported release
710
Status
CLOSED PER
PE
NoPE
HIPER
YesHIPER
Special Attention
NoSpecatt / Xsystem
Submitted date
2019-02-12
Closed date
2019-02-27
Last modified date
2020-12-16
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
Fix is available
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Document Information
Modified date:
12 January 2021