floating point context handling on xen amd64 broken?

[Tobias Nygren <tnn%NetBSD.org@localhost>]

This simple test program nondeterministically fails to produce the
correct result for me if I run two or more processes in parallell:

#include <stdio.h>
#include <math.h>
int main(void) {
        double x;
        int i;
        x = 0;
        for (i = 1; i < 100000000; i++) {
                x += 1.0 / (double)i;
        }
        printf("got: %f\n", x);
        printf("ref: 18.997896\n");
}

I've attached my kernel config for reference.

-Tobias

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