On Fri, Jan 12, 2018 at 10:08:20PM -0800, Andy Lutomirski wrote: > Now this is quite a strange value to write to CR3. The 0x800 part > means that we're using the "user" variant of the address space that > would have ASID=0 and the 0x1000 bit being set corresponds to the user > pgdir, but this is nonsense, since the kernel never uses PCID 0 for > user mode. We always start at 1. The only exception is if > X86_FEATURE_PCID is off. But, if X86_FEATURE_PCID is off, then we > shouldn't be setting any PCID bits. My bad, I was under the impression the lower 12 bits would be ignored without PCID :/ > .Lwrcr3_\@: > /* Flip the PGD and ASID to the user version */ > orq $(PTI_SWITCH_MASK), \scratch_reg > mov \scratch_reg, %cr3 > .Lend_\@: > > That's bogus. PTI_SWITCH_MASK is 0x1800, which has PCID = 0x800. > This should probably use an alternative to select between 0x1000 and > 0x800 depending on X86_FEATURE_PCID or just use an entirely different > label for the !PCID case. ALTERNATIVE "orq $(PTI_SWITCH_PGTABLE_MASK), \scratch_reg", "orq $(PTI_SWITCH_MASK), \scratch_reg", X86_FEATURE_PCID Is not wanting to compile though; probably that whole alternative vs macro thing again :/