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Patch "KVM: x86: obey KVM_X86_QUIRK_CD_NW_CLEARED in kvm_set_cr0()" has been added to the 4.3-stable tree

PATCH [email protected] 1 participant 1 message Dec 7, 2015

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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 4.3-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-4.3 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

Quoted 1 line

From 879ae1880449c88db11c1ebdaedc2da79b2fe73f Mon Sep 17 00:00:00 2001

From: Laszlo Ersek <[email protected]>
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 <[email protected]>

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 <[email protected]>
Cc Alex Williamson <[email protected]>
Reviewed-by Xiao Guangrong <[email protected]>
Tested-by Janusz Mocek <[email protected]>
Signed-off-by Laszlo Ersek <[email protected]>#
Signed-off-by Paolo Bonzini <[email protected]>
Signed-off-by Greg Kroah-Hartman <[email protected]>
---
 arch/x86/kvm/x86.c |    4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)
arch/x86/kvm/x86.c +3 -1
@@ -622,7 +622,9 @@ 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 [email protected] are

queue-4.3/kvm-x86-handle-smbase-as-physical-address-in-rsm.patch queue-4.3/kvm-x86-obey-kvm_x86_quirk_cd_nw_cleared-in-kvm_set_cr0.patch queue-4.3/x86-setup-fix-low-identity-map-for-2gb-kernel-range.patch queue-4.3/kvm-x86-allow-rsm-from-64-bit-mode.patch queue-4.3/kvm-x86-add-read_phys-to-x86_emulate_ops.patch