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authorPaolo Bonzini <pbonzini@redhat.com>2019-11-04 12:22:02 +0100
committerThomas Gleixner <tglx@linutronix.de>2019-11-04 12:22:02 +0100
commitb8e8c8303ff28c61046a4d0f6ea99aea609a7dc0 (patch)
treef5e0c8bb8b968eb158c07b274d9fdc465fdf95e8 /Documentation/admin-guide/kernel-parameters.txt
parent731dc9df975a5da21237a18c3384f811a7a41cc6 (diff)
kvm: mmu: ITLB_MULTIHIT mitigation
With some Intel processors, putting the same virtual address in the TLB as both a 4 KiB and 2 MiB page can confuse the instruction fetch unit and cause the processor to issue a machine check resulting in a CPU lockup. Unfortunately when EPT page tables use huge pages, it is possible for a malicious guest to cause this situation. Add a knob to mark huge pages as non-executable. When the nx_huge_pages parameter is enabled (and we are using EPT), all huge pages are marked as NX. If the guest attempts to execute in one of those pages, the page is broken down into 4K pages, which are then marked executable. This is not an issue for shadow paging (except nested EPT), because then the host is in control of TLB flushes and the problematic situation cannot happen. With nested EPT, again the nested guest can cause problems shadow and direct EPT is treated in the same way. [ tglx: Fixup default to auto and massage wording a bit ] Originally-by: Junaid Shahid <junaids@google.com> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com> Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Diffstat (limited to 'Documentation/admin-guide/kernel-parameters.txt')
-rw-r--r--Documentation/admin-guide/kernel-parameters.txt19
1 files changed, 19 insertions, 0 deletions
diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index fa8f03ddff24..9d5f123cc218 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -2055,6 +2055,19 @@
KVM MMU at runtime.
Default is 0 (off)
+ kvm.nx_huge_pages=
+ [KVM] Controls the software workaround for the
+ X86_BUG_ITLB_MULTIHIT bug.
+ force : Always deploy workaround.
+ off : Never deploy workaround.
+ auto : Deploy workaround based on the presence of
+ X86_BUG_ITLB_MULTIHIT.
+
+ Default is 'auto'.
+
+ If the software workaround is enabled for the host,
+ guests do need not to enable it for nested guests.
+
kvm-amd.nested= [KVM,AMD] Allow nested virtualization in KVM/SVM.
Default is 1 (enabled)
@@ -2637,6 +2650,12 @@
l1tf=off [X86]
mds=off [X86]
tsx_async_abort=off [X86]
+ kvm.nx_huge_pages=off [X86]
+
+ Exceptions:
+ This does not have any effect on
+ kvm.nx_huge_pages when
+ kvm.nx_huge_pages=force.
auto (default)
Mitigate all CPU vulnerabilities, but leave SMT