Re: [PATCH v2 1/4] xl: Add support for ignore_msrs option

[Julien Grall <julien@xen.org>]

Hi Boris,

On 20/01/2021 22:49, Boris Ostrovsky wrote:
> This option allows guest administrator specify what should happen when
> guest accesses an MSR which is not explicitly emulated by the hypervisor.
> 
> Signed-off-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
> ---
>   docs/man/xl.cfg.5.pod.in         | 20 +++++++++++++++++++-
>   tools/libs/light/libxl_types.idl |  7 +++++++
>   tools/xl/xl_parse.c              |  7 +++++++
>   3 files changed, 33 insertions(+), 1 deletion(-)
> 
> diff --git a/docs/man/xl.cfg.5.pod.in b/docs/man/xl.cfg.5.pod.in
> index c8e017f950de..96ce97c42cab 100644
> --- a/docs/man/xl.cfg.5.pod.in
> +++ b/docs/man/xl.cfg.5.pod.in
> @@ -2044,7 +2044,25 @@ Do not provide a VM generation ID.
>   See also "Virtual Machine Generation ID" by Microsoft:
>   L<https://docs.microsoft.com/en-us/windows/win32/hyperv_v2/virtual-machine-generation-identifier>
>   
> -=back
> +=over
> +
> +=item B<ignore_msrs="STRING">
> +
> +Determine hypervisor behavior on accesses to MSRs that are not emulated by the hypervisor.

The description of the feature looks very x86 focus. Yet, it seems to be 
defined as a generic one.

Could you clarify whether this is intended to be re-usable by other 
architectures?

> +
> +=over 4
> +
> +=item B<never>
> +
> +Issue a warning to the log and #GP to the guest. This is default.
> +
> +=item B<silent>
> +
> +MSR reads return 0, MSR writes are ignored. No warnings to the log.
> +
> +=item B<verbose>
> +
> +Similar to B<silent> but a warning is written.
>   
>   =head3 Guest Virtual Time Controls
>   
> diff --git a/tools/libs/light/libxl_types.idl b/tools/libs/light/libxl_types.idl
> index 05324736b744..7b5fef771ee8 100644
> --- a/tools/libs/light/libxl_types.idl
> +++ b/tools/libs/light/libxl_types.idl
> @@ -477,6 +477,12 @@ libxl_tee_type = Enumeration("tee_type", [
>       (1, "optee")
>       ], init_val = "LIBXL_TEE_TYPE_NONE")
>   
> +libxl_ignore_msrs = Enumeration("ignore_msrs", [
> +    (0, "never"),
> +    (1, "silent"),
> +    (2, "verbose"),
> +    ], init_val = "LIBXL_IGNORE_MSRS_NEVER")
> +
>   libxl_rdm_reserve = Struct("rdm_reserve", [
>       ("strategy",    libxl_rdm_reserve_strategy),
>       ("policy",      libxl_rdm_reserve_policy),
> @@ -559,6 +565,7 @@ libxl_domain_build_info = Struct("domain_build_info",[
>       ("apic",             libxl_defbool),
>       ("dm_restrict",      libxl_defbool),
>       ("tee",              libxl_tee_type),
> +    ("ignore_msrs",      libxl_ignore_msrs),
>       ("u", KeyedUnion(None, libxl_domain_type, "type",
>                   [("hvm", Struct(None, [("firmware",         string),
>                                          ("bios",             libxl_bios_type),
> diff --git a/tools/xl/xl_parse.c b/tools/xl/xl_parse.c
> index 4ebf39620ae7..942086c3f41d 100644
> --- a/tools/xl/xl_parse.c
> +++ b/tools/xl/xl_parse.c
> @@ -2732,6 +2732,13 @@ skip_usbdev:
>           }
>       }
>   
> +    if (!xlu_cfg_get_string(config, "ignore_msrs", &buf, 0)) {
> +        if (libxl_ignore_msrs_from_string(buf, &b_info->ignore_msrs)) {
> +           fprintf(stderr, "ERROR: invalid value \"%s\" for \"ignore_msrs\"\n", buf);
> +           exit(1);
> +        }
> +    }
> +
>       parse_vkb_list(config, d_config);
>   
>       xlu_cfg_get_defbool(config, "xend_suspend_evtchn_compat",
> 

Cheers,

-- 
Julien Grall