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>>>> >>>> + if ( !compat ) >>>> + { >>>> + if ( c(debugreg[6]) != (uint32_t)c(debugreg[6]) || >>>> + c(debugreg[7]) != (uint32_t)c(debugreg[7]) ) >>>> + return -EINVAL; >>>> + } >>>> + >>>> if ( is_pv_domain(d) ) >>>> { >>>> + /* >>>> + * Prior to Xen 4.11, dr5 was used to hold the emulated-only >>>> + * subset of dr7, and dr4 was unused. >>>> + * >>>> + * In Xen 4.11 and later, dr4/5 are written as zero, ignored for >>>> + * backwards compatibility, and dr7 emulation is handled >>>> + * internally. >>>> + */ >>>> + for ( i = 0; i < ARRAY_SIZE(v->arch.dr); i++ ) >>>> + if ( !access_ok(c(debugreg[i]), sizeof(long)) ) >>> Don't you mean __addr_ok() here, i.e. not including the >>> is_compat_arg_xlat_range() check? (Else I would have asked why >>> sizeof(long), but that question resolves itself with using the other >>> macro.) >> For now, I'm simply moving a check from set_debugreg() earlier in >> arch_set_info_guest(). >> >> I think it would be beneficial to keep that change independent. > Hmm, difficult. I'd be okay if you indeed moved the other check. But > you duplicate it here, and duplicating questionable code is, well, > questionable. It can't be removed in set_debugreg() because that's used in other paths too. And the error from set_debugreg() can't fail arch_set_info_guest() because that introduces a failure after mutation of the vCPU state. This isn't a fastpath.  It's used approximately once per vCPU lifetime. ~Andrew