On 2/15/23 3:31 AM, Jan Beulich wrote:
On 15.02.2023 01:07, Boris Ostrovsky wrote:
On 2/14/23 6:53 PM, Boris Ostrovsky wrote:
On 2/14/23 11:13 AM, Jan Beulich wrote:
--- a/arch/x86/kernel/cpu/bugs.c
+++ b/arch/x86/kernel/cpu/bugs.c
@@ -18,6 +18,8 @@
#include <linux/pgtable.h>
#include <linux/bpf.h>
+#include <xen/xen.h>
+
#include <asm/spec-ctrl.h>
#include <asm/cmdline.h>
#include <asm/bugs.h>
@@ -32,6 +34,7 @@
#include <asm/intel-family.h>
#include <asm/e820/api.h>
#include <asm/hypervisor.h>
+#include <asm/xen/hypervisor.h>
#include <asm/tlbflush.h>
#include "cpu.h"
@@ -934,7 +937,8 @@ do_cmd_auto:
break;
case RETBLEED_MITIGATION_IBPB:
- setup_force_cpu_cap(X86_FEATURE_ENTRY_IBPB);
+ if (!xen_pv_domain() || xen_vm_assist_ibpb(true))
Is this going to compile without CONFIG_XEN?
Yes. The declaration of xen_vm_assist_ibpb() is visible (satisfying
the compiler) and DCE will eliminate the call to the function due to
xen_pv_domain() being constant "false" in that case, avoiding any
linking issues. The interesting case here really is building with
XEN but without XEN_PV: That's why I needed to put the function in
enlighten.c. This wouldn't be needed if xen_pv_domain() was also
constant "false" in that case (just like xen_pvh_domain() is when
!XEN_PVH).
I also think these two conditions should be wrapped into something to limit
exposure of non-Xen code to Xen-specific primitives.
I would have done so, if I had any halfway sensible idea on how to
go about doing so in this particular case. In the absence of that it
looked okay-ish to me to reference Xen functions directly here.
Oh, and this needs x86 maintainers.
Eventually yes. But I would prefer to sort the above question first
(which I'm sure would have been raised by them, in perhaps more
harsh a way), hence the initially limited exposure.
I also think there is a bit of a disconnect between how the mitigation is reported in the
log/sysfs (retbleed_mitigation is RETBLEED_MITIGATION_IBPB, so "Mitigation:
IBPB") and, for example, lscpu (since X86_FEATURE_ENTRY_IBPB is not set anymore).
-boris
