On Thu, Feb 1, 2018 at 1:59 PM, KarimAllah Ahmed <karahmed@xxxxxxxxx> wrote: > [ Based on a patch from Ashok Raj <ashok.raj@xxxxxxxxx> ] > > Add direct access to MSR_IA32_SPEC_CTRL for guests. This is needed for > guests that will only mitigate Spectre V2 through IBRS+IBPB and will not > be using a retpoline+IBPB based approach. > > To avoid the overhead of saving and restoring the MSR_IA32_SPEC_CTRL for > guests that do not actually use the MSR, only start saving and restoring > when a non-zero is written to it. > > No attempt is made to handle STIBP here, intentionally. Filtering STIBP > may be added in a future patch, which may require trapping all writes > if we don't want to pass it through directly to the guest. > > [dwmw2: Clean up CPUID bits, save/restore manually, handle reset] > > Cc: Asit Mallick <asit.k.mallick@xxxxxxxxx> > Cc: Arjan Van De Ven <arjan.van.de.ven@xxxxxxxxx> > Cc: Dave Hansen <dave.hansen@xxxxxxxxx> > Cc: Andi Kleen <ak@xxxxxxxxxxxxxxx> > Cc: Andrea Arcangeli <aarcange@xxxxxxxxxx> > Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> > Cc: Tim Chen <tim.c.chen@xxxxxxxxxxxxxxx> > Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx> > Cc: Dan Williams <dan.j.williams@xxxxxxxxx> > Cc: Jun Nakajima <jun.nakajima@xxxxxxxxx> > Cc: Paolo Bonzini <pbonzini@xxxxxxxxxx> > Cc: David Woodhouse <dwmw@xxxxxxxxxxxx> > Cc: Greg KH <gregkh@xxxxxxxxxxxxxxxxxxx> > Cc: Andy Lutomirski <luto@xxxxxxxxxx> > Cc: Ashok Raj <ashok.raj@xxxxxxxxx> > Signed-off-by: KarimAllah Ahmed <karahmed@xxxxxxxxx> > Signed-off-by: David Woodhouse <dwmw@xxxxxxxxxxxx> Reviewed-by: Jim Mattson <jmattson@xxxxxxxxxx>
