On 01/29/18 08:37, Andy Lutomirski wrote: > > That's what I thought, too, and the SDM does say that, but the SDM > says all kinds of not-quite-correct things about segmentation. > >> It is pretty much scratch space (I have >> suggested using it for the gsbase once all those issues get sorted out, >> because it lets the paranoid code do something like: >> >> rdgsbase %rax >> push %rax /* Save old gsbase */ >> push %rax /* Reserve space on stack */ >> sgdt -2(%rsp) /* We don't care about the limit */ >> pop %rax /* %rax <- gdtbase */ >> mov (%rax),%rax /* GDT[0] holds the gsbase for this cpu */ >> wrgsbase %rax > > That will utterly suck on non-UMIP machines that have > hypervisor-provided UMIP emulation. > Is that a valid thing to optimize for, especially given that paranoid entries aren't the most common anyway? -hpa -- To unsubscribe from this list: send the line "unsubscribe linux-kselftest" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
