untrusted comment: verify with openbsd-64-base.pub
RWQq6XmS4eDAcVNfNTRIqZkmpi+rgkRnJbzXl8hN52NJQXoxD2NwnMResMpjH3fAEMtYZfipi1VskqO9TboD+1iLPx1yMqqNMAU=

OpenBSD 6.4 errata 022, Sep 2, 2019:

Resume forgot to restore MSR/PAT configuration.

Apply by doing:
    signify -Vep /etc/signify/openbsd-64-base.pub -x 022_resume.patch.sig \
        -m - | (cd /usr/src && patch -p0)

And then rebuild and install a new kernel:
    KK=`sysctl -n kern.osversion | cut -d# -f1`
    cd /usr/src/sys/arch/`machine`/compile/$KK
    make obj
    make config
    make
    make install

Index: sys/arch/amd64/amd64/acpi_machdep.c
===================================================================
RCS file: /cvs/src/sys/arch/amd64/amd64/acpi_machdep.c,v
diff -u -p -u -r1.85 acpi_machdep.c
--- sys/arch/amd64/amd64/acpi_machdep.c	19 Aug 2018 08:23:47 -0000	1.85
+++ sys/arch/amd64/amd64/acpi_machdep.c	20 Aug 2019 02:25:47 -0000
@@ -381,6 +381,8 @@ acpi_sleep_clocks(struct acpi_softc *sc,
 void
 acpi_resume_clocks(struct acpi_softc *sc)
 {
+	cpu_init_msrs(&cpu_info_primary);
+
 #if NISA > 0
 	i8259_default_setup();
 #endif