> From: Sean Christopherson <[email protected]> > Date: Mon, 26 Oct 2026 07:37:03 -0700 > Subject: [PATCH] KVM: x86: Don't bother loading host values for SYSCALL MSRs > when FRED is in use > > Elide the WRMSRs for the SYSCALL MSRs when returning to userspace if FRED > is in use, in which case said MSRs are never actually used in Linux. > > Note, KVM never saves/restores MSR_CSTAR via the user-return MSR mechanism, > as the MSR is unused by Intel/VMX hardware, and SVM unconditionally context > switches the MSR via a dedicated VMCB field (along with all other SYSCALL > MSRs). Include MSR_CSTAR to provide a contiguous range of values in the > case statements, e.g. so that the compiler can optimize the case statements > into a simple bounds checks. >
Sean, I assume you will post this separately. I don't think it depends on anything in this series. Please let me know if you want me to do anything additional here. > Suggested-by: Xin Li (Intel) <[email protected]> BTW, Xin no longer works at Intel. For any of his *new* contributions to the kernel, he has been using: Xin Li <[email protected]> > Signed-off-by: Sean Christopherson <[email protected]> > --- > arch/x86/kvm/msrs.c | 20 +++++++++++++++++++- > 1 file changed, 19 insertions(+), 1 deletion(-) > >
