Dear ArmPkg maintainer, Way back in SVN rev 12024 (July 18 2011!) a change was made to the UncachedMemoryAllocationLib to use DXE Services instead of the CPU AP driver to change the cacheability of allocated pages. However the function to free these pages was not updated and still called the CPU AP driver directly to restore cacheability. This causes the DXE GCD and page tables to get out of sync.
When the library was first created, a choice was made to store the previous cacheability attributes in a global variable (gAttributes). This global stores the old attributes from the last allocation, obtained from gDS->GetMemorySpaceAttributes, overwriting the previous value. Since the GCD still thinks these pages are uncacheable, the next time gDS->GetMemorySpaceAttributes is called for the address, it returns an uncacheable value and stores it in gAttributes. Then any subsequent calls to UncachedFreeAlignedPages will "restore" the cacheability value to an uncached value. These pages are returned to the free page pool but are really still uncached causing serious performance degradation in a non-deterministic manner. The fix is simple, route both the setting and restoring of cacheability through DXE Services/GCD and stop using the CPU AP directly. The patch also removes all references to the CPU AP which eliminates the need for a library constructor. Contributed-under: TianoCore Contribution Agreement 1.0 Signed-off-by: Eugene Cohen <eug...@hp.com<mailto:eug...@hp.com>> Reviewed-by: Senthil Ramakrishnan <senthil.ramakrish...@hp.com<mailto:senthil.ramakrish...@hp.com>> Thanks, Eugene
arm_uncached_free_fix.patch
Description: arm_uncached_free_fix.patch
------------------------------------------------------------------------------ See everything from the browser to the database with AppDynamics Get end-to-end visibility with application monitoring from AppDynamics Isolate bottlenecks and diagnose root cause in seconds. Start your free trial of AppDynamics Pro today! http://pubads.g.doubleclick.net/gampad/clk?id=48808831&iu=/4140/ostg.clktrk
_______________________________________________ edk2-devel mailing list edk2-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/edk2-devel
