Re: [Qemu-devel] [SeaBIOS] [PATCH v2] fw/msr_feature_control: add support to set MSR_IA32_FEATURE_CONTROL

[Kevin O'Connor]

On Fri, Jun 17, 2016 at 03:20:10PM +0800, Haozhong Zhang wrote:
> OS usually expects BIOS to set certain bits in MSR_IA32_FEATURE_CONTROL
> for some features (e.g. VMX and LMCE). QEMU provides a fw_cfg file
> "etc/msr_feature_control" to advise bits that should be set in
> MSR_IA32_FEATURE_CONTROL. If this file exists, SeaBIOS will set the
> advised bits in that MSR.

Thanks - see my comments below.

> --- /dev/null
> +++ b/src/fw/msr_feature_control.c
> @@ -0,0 +1,16 @@
> +#include "util.h" // msr_feature_control_setup, wrmsr_smp
> +#include "romfile.h" // romfile_find
> +
> +#define MSR_IA32_FEATURE_CONTROL 0x0000003a
> +
> +void msr_feature_control_setup(void)
> +{
> +    struct romfile_s *f = romfile_find("etc/msr_feature_control");
> +    if (!f)
> +        return;
> +
> +    u64 feature_control_bits;
> +    f->copy(f, &feature_control_bits, sizeof(feature_control_bits));
> +    if (feature_control_bits)
> +        wrmsr_smp(MSR_IA32_FEATURE_CONTROL, feature_control_bits);
> +}

Can you use romfile_loadint() instead?  Something like:

    u64 feature_control_bits = romfile_loadint("etc/msr_feature_control", 0);
    if (feature_control_bits)
        wrmsr_smp(MSR_IA32_FEATURE_CONTROL, feature_control_bits);

That should avoid the need for the separate romfile_find() call and it
has the added benefit of additional sanity checks.

Also, I think this code is small enough it can be placed directly in
paravirt.c and does not need its own c file.

-Kevin