| Message ID | 6b594869-1c64-93a3-7f19-f7374b62eeee@suse.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | xen-detect: make CPUID fallback CPUID-faulting aware | expand |
On Wed, Oct 14, 2020 at 05:23:23PM +0200, Jan Beulich wrote: > Relying on presence / absence of hypervisor leaves in raw / escaped > CPUID output cannot be used to tell apart PV and HVM on CPUID faulting > capable hardware. Utilize a PV-only feature flag to avoid false positive > HVM detection. > > While at it also short circuit the main detection loop: For PV, only > the base group of leaves can possibly hold hypervisor information. > > Signed-off-by: Jan Beulich <jbeulich@suse.com> Acked-by: Wei Liu <wl@xen.org>
--- a/tools/misc/xen-detect.c +++ b/tools/misc/xen-detect.c @@ -83,11 +83,31 @@ static int check_for_xen(int pv_context) if ( !strcmp("XenVMMXenVMM", signature) && (regs[0] >= (base + 2)) ) goto found; + + /* Higher base addresses are possible only with HVM. */ + if ( pv_context ) + break; } return 0; found: + /* + * On CPUID faulting capable hardware even un-escaped CPUID will return + * the hypervisor leaves. Need to further distinguish modes. + */ + if ( !pv_context ) + { + /* + * XEN_CPUID_FEAT1_MMU_PT_UPDATE_PRESERVE_AD is a PV-only feature + * pre-dating CPUID faulting support in Xen. Hence we can use it to + * tell whether we shouldn't report "success" to our caller here. + */ + cpuid(base + 2, regs, 0); + if ( regs[2] & (1u << 0) ) + return 0; + } + cpuid(base + 1, regs, pv_context); if ( regs[0] ) {
Relying on presence / absence of hypervisor leaves in raw / escaped CPUID output cannot be used to tell apart PV and HVM on CPUID faulting capable hardware. Utilize a PV-only feature flag to avoid false positive HVM detection. While at it also short circuit the main detection loop: For PV, only the base group of leaves can possibly hold hypervisor information. Signed-off-by: Jan Beulich <jbeulich@suse.com>