Linux kernel mirror (for testing)
git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
kernel
os
linux
KVM: SVM: Skip OSVW MSR reads if KVM is treating all errata as present
Don't bother reading the OSVW MSRs if osvw_len is already zero, i.e. if
KVM is already treating all errata as present, in which case the positive
path of the if-statement is one giant nop.
Opportunistically update the comment to more thoroughly explain how the
MSRs work and why the code does what it does.
Link: https://patch.msgid.link/20251113231420.1695919-3-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>
+12
-2
+12
-2
arch/x86/kvm/svm/svm.c
+12
-2
arch/x86/kvm/svm/svm.c
···
543
543
544
544
545
545
/*
546
-
* Get OSVW bits.
546
+
* Get OS-Visible Workarounds (OSVW) bits.
547
547
*
548
548
* Note that it is possible to have a system with mixed processor
549
549
* revisions and therefore different OSVW bits. If bits are not the same
550
550
* on different processors then choose the worst case (i.e. if erratum
551
551
* is present on one processor and not on another then assume that the
552
552
* erratum is present everywhere).
553
+
*
554
+
* Note #2! The OSVW MSRs are used to communciate that an erratum is
555
+
* NOT present! Software must assume erratum as present if its bit is
556
+
* set in OSVW_STATUS *or* the bit number exceeds OSVW_ID_LENGTH. If
557
+
* either RDMSR fails, simply zero out the length to treat all errata
558
+
* as being present. Similarly, use the *minimum* length across all
559
+
* CPUs, not the maximum length.
560
+
*
561
+
* If the length is zero, then is KVM already treating all errata as
562
+
* being present and there's nothing left to do.
553
563
*/
554
-
if (cpu_has(&boot_cpu_data, X86_FEATURE_OSVW)) {
564
+
if (osvw_len && cpu_has(&boot_cpu_data, X86_FEATURE_OSVW)) {
555
565
u64 len, status = 0;
556
566
int err;
557
567