Re: [PATCH] x86/Xen: make use of IBPB controlling VM assist

[Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>]

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?


I also think these two conditions should be wrapped into something to limit 
exposure of non-Xen code to Xen-specific primitives.


-boris


> +                       setup_force_cpu_cap(X86_FEATURE_ENTRY_IBPB);
>                 mitigate_smt = true;
>                 break;