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From: Joerg Roedel <jroedel@suse.de>
To: speck@linutronix.de
Subject: [MODERATED] Re: ***UNCHECKED*** [PATCH v7 3/5] NX 3
Date: Fri, 25 Oct 2019 10:37:39 +0200	[thread overview]
Message-ID: <20191025083739.GC7069@suse.de> (raw)
In-Reply-To: <1571934870-34323-4-git-send-email-pbonzini@redhat.com>

Hi Paolo,

On Thu, Oct 24, 2019 at 06:34:28PM +0200, speck for Paolo Bonzini wrote:
>  Documentation/admin-guide/kernel-parameters.txt |  11 ++
>  arch/x86/include/asm/kvm_host.h                 |   2 +
>  arch/x86/kernel/cpu/bugs.c                      |  13 ++-
>  arch/x86/kvm/mmu.c                              | 135 ++++++++++++++++++++++--
>  arch/x86/kvm/paging_tmpl.h                      |  29 +++--
>  arch/x86/kvm/x86.c                              |   9 ++
>  6 files changed, 186 insertions(+), 13 deletions(-)

I did some testing on 5.4-rc4 with these patches and they break the
ept=off case on some machines, especially those with the load_ia32_efer
capability:

	kvm [10312]: vcpu0, guest rIP: 0xffffffff810643f8 disabled perfctr wrmsr: 0xc2 data 0xffff
	walk_shadow_page_get_mmio_spte: detect reserved bits on spte, addr 0xbffbffd8, dump hierarchy:
	------ spte 0x80000003ab000ce7 level 2.

The reason is that during early guest boot KVM direct-maps the guest
memory with a PAE page-table and pages there get the NX bit set. But the
guest has EFER.NX=0, which causes the NX-bit to be reserved.

I fixed it with this diff:

diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index e7970a2e8eae..6e9380a0ca41 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -997,7 +997,7 @@ static bool update_transition_efer(struct vcpu_vmx *vmx, int efer_offset)
 	 * On CPUs that support "load IA32_EFER", always switch EFER
 	 * atomically, since it's faster than switching it manually.
 	 */
-	if (cpu_has_load_ia32_efer() ||
+	if ((cpu_has_load_ia32_efer() && (guest_efer & EFER_NX)) ||
 	    (enable_ept && ((vmx->vcpu.arch.efer ^ host_efer) & EFER_NX))) {
 		if (!(guest_efer & EFER_LMA))
 			guest_efer &= ~EFER_LME;


Regards,

	Joerg

  reply	other threads:[~2019-10-25  8:37 UTC|newest]

Thread overview: 18+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-10-24 16:34 [MODERATED] [PATCH v7 0/5] NX 0 Paolo Bonzini
2019-10-24 16:34 ` [MODERATED] [PATCH v7 1/5] NX 1 Paolo Bonzini
2019-10-30 18:38   ` [MODERATED] " Josh Poimboeuf
2019-10-31 11:05     ` Paolo Bonzini
2019-10-24 16:34 ` [MODERATED] [PATCH v7 2/5] NX 2 Paolo Bonzini
2019-10-24 16:34 ` [MODERATED] [PATCH v7 3/5] NX 3 Paolo Bonzini
2019-10-25  8:37   ` Joerg Roedel [this message]
2019-10-25  8:48     ` [MODERATED] Re: ***UNCHECKED*** " Paolo Bonzini
2019-10-25  9:03       ` [MODERATED] Re: ***UNCHECKED*** " Joerg Roedel
2019-10-25  9:08         ` Paolo Bonzini
2019-10-25  9:45           ` [MODERATED] Re: ***UNCHECKED*** " Joerg Roedel
2019-10-25 10:39             ` Paolo Bonzini
2019-10-29 20:33               ` mark gross
2019-10-31 11:02                 ` Paolo Bonzini
2019-10-24 16:34 ` [MODERATED] [PATCH v7 4/5] NX 4 Paolo Bonzini
2019-10-24 16:34 ` [MODERATED] [PATCH v7 5/5] NX 5 Paolo Bonzini
2019-10-24 18:27 ` [MODERATED] Re: [PATCH v7 0/5] NX 0 Ben Hutchings
2019-10-24 18:56   ` Paolo Bonzini

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