tree 5cbf75bf302b4696acfc72034f58a694569a8eaf
parent d1ae67f626c5ed5729e1d8212834291b409d26df
author Alex Williamson <alex.williamson@redhat.com> 1408052379 -0600
committer Paolo Bonzini <pbonzini@redhat.com> 1408985622 +0200

x86: Clear MTRRs on vCPU reset

The SDM specifies (June 2014 Vol3 11.11.5):

    On a hardware reset, the P6 and more recent processors clear the
    valid flags in variable-range MTRRs and clear the E flag in the
    IA32_MTRR_DEF_TYPE MSR to disable all MTRRs. All other bits in the
    MTRRs are undefined.

We currently do none of that, so whatever MTRR settings you had prior
to reset is what you have after reset.  Usually this doesn't matter
because KVM often ignores the guest mappings and uses write-back
anyway.  However, if you have an assigned device and an IOMMU that
allows NoSnoop for that device, KVM defers to the guest memory
mappings which are now stale after reset.  The result is that OVMF
rebooting on such a configuration takes a full minute to LZMA
decompress the firmware volume, a process that is nearly instant on
the initial boot.

Signed-off-by: Alex Williamson <alex.williamson@redhat.com>
Reviewed-by: Laszlo Ersek <lersek@redhat.com>
Cc: qemu-stable@nongnu.org
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>