https://community.intel.com/t5/Intel-Business-Client-Software/x86-instructions-kernel-or-user-mode/m-p/1753061#M7320 <P>i have learned x86 architecture and understood protected mode and real mode. However never gave thought that there will be instructions that may work in kernel mode and not in user mode. I never came across if such restriction exists. Pls let me know if such restriction or set of instructions exist that only works in kernel mode and not user mode. cmpxchg and respective instructions i suspected after read in datasheet that these may not work in user mode. Pls confirm this. There is no specific i found in datasheet that explains it. i have referred datasheet&nbsp;<A title="x86 datasheets" href="https://www.intel.com/content/www/us/en/developer/articles/technical/intel-sdm.html" target="_self">https://www.intel.com/content/www/us/en/developer/articles/technical/intel-sdm.html</A>&nbsp;I might missed something particular pls help me.</P> Fri, 03 Jul 2026 19:35:46 GMT prasadkaka 2026-07-03T19:35:46Z https://community.intel.com/t5/Intel-Business-Client-Software/x86-instructions-kernel-or-user-mode/m-p/1753061#M7320 <P>i have learned x86 architecture and understood protected mode and real mode. However never gave thought that there will be instructions that may work in kernel mode and not in user mode. I never came across if such restriction exists. Pls let me know if such restriction or set of instructions exist that only works in kernel mode and not user mode. cmpxchg and respective instructions i suspected after read in datasheet that these may not work in user mode. Pls confirm this. There is no specific i found in datasheet that explains it. i have referred datasheet&nbsp;<A title="x86 datasheets" href="https://www.intel.com/content/www/us/en/developer/articles/technical/intel-sdm.html" target="_self">https://www.intel.com/content/www/us/en/developer/articles/technical/intel-sdm.html</A>&nbsp;I might missed something particular pls help me.</P> Fri, 03 Jul 2026 19:35:46 GMT https://community.intel.com/t5/Intel-Business-Client-Software/x86-instructions-kernel-or-user-mode/m-p/1753061#M7320 prasadkaka 2026-07-03T19:35:46Z