Patch "KVM: x86: obey KVM_X86_QUIRK_CD_NW_CLEARED in kvm_set_cr0()" has been added to the 4.2-stable tree

[<gregkh@linuxfoundation.org>]

This is a note to let you know that I've just added the patch titled

    KVM: x86: obey KVM_X86_QUIRK_CD_NW_CLEARED in kvm_set_cr0()

to the 4.2-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     kvm-x86-obey-kvm_x86_quirk_cd_nw_cleared-in-kvm_set_cr0.patch
and it can be found in the queue-4.2 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@vger.kernel.org> know about it.


>From 879ae1880449c88db11c1ebdaedc2da79b2fe73f Mon Sep 17 00:00:00 2001
From: Laszlo Ersek <lersek@redhat.com>
Date: Wed, 4 Nov 2015 12:54:41 +0100
Subject: KVM: x86: obey KVM_X86_QUIRK_CD_NW_CLEARED in kvm_set_cr0()

From: Laszlo Ersek <lersek@redhat.com>

commit 879ae1880449c88db11c1ebdaedc2da79b2fe73f upstream.

Commit b18d5431acc7 ("KVM: x86: fix CR0.CD virtualization") was
technically correct, but it broke OVMF guests by slowing down various
parts of the firmware.

Commit fb279950ba02 ("KVM: vmx: obey KVM_QUIRK_CD_NW_CLEARED") quirked the
first function modified by b18d5431acc7, vmx_get_mt_mask(), for OVMF's
sake. This restored the speed of the OVMF code that runs before
PlatformPei (including the memory intensive LZMA decompression in SEC).

This patch extends the quirk to the second function modified by
b18d5431acc7, kvm_set_cr0(). It eliminates the intrusive slowdown that
hits the EFI_MP_SERVICES_PROTOCOL implementation of edk2's
UefiCpuPkg/CpuDxe -- which is built into OVMF --, when CpuDxe starts up
all APs at once for initialization, in order to count them.

We also carry over the kvm_arch_has_noncoherent_dma() sub-condition from
the other half of the original commit b18d5431acc7.

Fixes: b18d5431acc7a2fd22767925f3a6f597aa4bd29e
Cc: Jordan Justen <jordan.l.justen@intel.com>
Cc: Alex Williamson <alex.williamson@redhat.com>
Reviewed-by: Xiao Guangrong <guangrong.xiao@linux.intel.com>
Tested-by: Janusz Mocek <januszmk6@gmail.com>
Signed-off-by: Laszlo Ersek <lersek@redhat.com>#
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 arch/x86/kvm/x86.c |    4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -621,7 +621,9 @@ int kvm_set_cr0(struct kvm_vcpu *vcpu, u
 	if ((cr0 ^ old_cr0) & update_bits)
 		kvm_mmu_reset_context(vcpu);
 
-	if ((cr0 ^ old_cr0) & X86_CR0_CD)
+	if (((cr0 ^ old_cr0) & X86_CR0_CD) &&
+	    kvm_arch_has_noncoherent_dma(vcpu->kvm) &&
+	    !kvm_check_has_quirk(vcpu->kvm, KVM_X86_QUIRK_CD_NW_CLEARED))
 		kvm_zap_gfn_range(vcpu->kvm, 0, ~0ULL);
 
 	return 0;


Patches currently in stable-queue which might be from lersek@redhat.com are

queue-4.2/kvm-x86-handle-smbase-as-physical-address-in-rsm.patch
queue-4.2/kvm-x86-obey-kvm_x86_quirk_cd_nw_cleared-in-kvm_set_cr0.patch
queue-4.2/x86-setup-fix-low-identity-map-for-2gb-kernel-range.patch
queue-4.2/kvm-x86-allow-rsm-from-64-bit-mode.patch
queue-4.2/x86-setup-extend-low-identity-map-to-cover-whole-kernel-range.patch
queue-4.2/kvm-x86-add-read_phys-to-x86_emulate_ops.patch