On 3/10/22 06:32, David Laight wrote: >> UAI allows software to store a tag in the upper 7 bits of a logical >> address [63:57]. When enabled, the processor will suppress the >> traditional canonical address checks on the addresses. More information >> about UAI can be found in section 5.10 of 'AMD64 Architecture >> Programmer's Manual, Vol 2: System Programming' which is available from >> >> https://bugzilla.kernel.org/attachment.cgi?id=300549 > Is that really allowing bit 63 to be used? > That is normally the user-kernel bit. > I can't help feeling that will just badly break things. Yeah, this does seem worrisome. The LAM approach[1] retains canonicality checking for bit 63. 1. https://www.intel.com/content/www/us/en/develop/download/intel-architecture-instruction-set-extensions-programming-reference.html
