On 11/01/2017 02:25 PM, Thomas Gleixner wrote: >> cr4 = this_cpu_read(cpu_tlbstate.cr4); >> - /* clear PGE */ >> - native_write_cr4(cr4 & ~X86_CR4_PGE); >> - /* write old PGE again and flush TLBs */ >> + /* >> + * This function is only called on systems that support X86_CR4_PGE >> + * and where always set X86_CR4_PGE. Warn if we are called without >> + * PGE set. >> + */ >> + WARN_ON_ONCE(!(cr4 & X86_CR4_PGE)); > Because if CR4_PGE is not set, this warning triggers. So this defeats the > toggle mode you are implementing.
The warning is there because there is probably plenty of *other* stuff that breaks if we have X86_FEATURE_PGE=1, but CR4.PGE=0. The point of this was to make this function do the right thing no matter what, but warn if it gets called in an unexpected way.
