kvm-x86-obey-KVM_X86_QUIRK_CD_NW_CLEARED-in-kvm_set_cr0.patch

   1 From 879ae1880449c88db11c1ebdaedc2da79b2fe73f Mon Sep 17 00:00:00 2001
   2 From: Laszlo Ersek <lersek@redhat.com>
   3 Date: Wed, 4 Nov 2015 12:54:41 +0100
   4 Subject: KVM: x86: obey KVM_X86_QUIRK_CD_NW_CLEARED in kvm_set_cr0()
   5
   6 Commit b18d5431acc7 ("KVM: x86: fix CR0.CD virtualization") was
   7 technically correct, but it broke OVMF guests by slowing down various
   8 parts of the firmware.
   9
  10 Commit fb279950ba02 ("KVM: vmx: obey KVM_QUIRK_CD_NW_CLEARED") quirked the
  11 first function modified by b18d5431acc7, vmx_get_mt_mask(), for OVMF's
  12 sake. This restored the speed of the OVMF code that runs before
  13 PlatformPei (including the memory intensive LZMA decompression in SEC).
  14
  15 This patch extends the quirk to the second function modified by
  16 b18d5431acc7, kvm_set_cr0(). It eliminates the intrusive slowdown that
  17 hits the EFI_MP_SERVICES_PROTOCOL implementation of edk2's
  18 UefiCpuPkg/CpuDxe -- which is built into OVMF --, when CpuDxe starts up
  19 all APs at once for initialization, in order to count them.
  20
  21 We also carry over the kvm_arch_has_noncoherent_dma() sub-condition from
  22 the other half of the original commit b18d5431acc7.
  23
  24 Fixes: b18d5431acc7a2fd22767925f3a6f597aa4bd29e
  25 Cc: stable@vger.kernel.org
  26 Cc: Jordan Justen <jordan.l.justen@intel.com>
  27 Cc: Alex Williamson <alex.williamson@redhat.com>
  28 Reviewed-by: Xiao Guangrong <guangrong.xiao@linux.intel.com>
  29 Tested-by: Janusz Mocek <januszmk6@gmail.com>
  30 Signed-off-by: Laszlo Ersek <lersek@redhat.com>#
  31 Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
  32 ---
  33  arch/x86/kvm/x86.c | 4 +++-
  34  1 file changed, 3 insertions(+), 1 deletion(-)
  35
  36 diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
  37 index a24bae0..30723a4 100644
  38 --- a/arch/x86/kvm/x86.c
  39 +++ b/arch/x86/kvm/x86.c
  40 @@ -625,7 +625,9 @@ int kvm_set_cr0(struct kvm_vcpu *vcpu, unsigned long cr0)
  41         if ((cr0 ^ old_cr0) & update_bits)
  42                 kvm_mmu_reset_context(vcpu);
  43
  44 -       if ((cr0 ^ old_cr0) & X86_CR0_CD)
  45 +       if (((cr0 ^ old_cr0) & X86_CR0_CD) &&
  46 +           kvm_arch_has_noncoherent_dma(vcpu->kvm) &&
  47 +           !kvm_check_has_quirk(vcpu->kvm, KVM_X86_QUIRK_CD_NW_CLEARED))
  48                 kvm_zap_gfn_range(vcpu->kvm, 0, ~0ULL);
  49
  50         return 0;
  51 --
  52 cgit v0.11.2
  53