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SubjectRe: [PATCH 2/2] x86/bugs: Fix the AMD SSBD usage of the SPEC_CTRL MSR
On Mon, Jul 02, 2018 at 04:36:02PM -0500, Tom Lendacky wrote:
> On AMD, the presence of the MSR_SPEC_CTRL feature does not imply that the
> SSBD mitigation support should use the SPEC_CTRL MSR. Other features could
> have caused the MSR_SPEC_CTRL feature to be set, while a different SSBD
> mitigation option is in place.
>
> Update the SSBD support to check for the actual SSBD features that will
> use the SPEC_CTRL MSR.
>
> Fixes: 6ac2f49edb1e ("x86/bugs: Add AMD's SPEC_CTRL MSR usage")
> Signed-off-by: Tom Lendacky <thomas.lendacky@amd.com>

Reviewed-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>

Thank you!
> ---
> arch/x86/kernel/cpu/bugs.c | 8 +++++---
> 1 file changed, 5 insertions(+), 3 deletions(-)
>
> diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c
> index 404df26..5c0ea39 100644
> --- a/arch/x86/kernel/cpu/bugs.c
> +++ b/arch/x86/kernel/cpu/bugs.c
> @@ -155,7 +155,8 @@ enum spectre_v2_mitigation_cmd {
> guestval |= guest_spec_ctrl & x86_spec_ctrl_mask;
>
> /* SSBD controlled in MSR_SPEC_CTRL */
> - if (static_cpu_has(X86_FEATURE_SPEC_CTRL_SSBD))
> + if (static_cpu_has(X86_FEATURE_SPEC_CTRL_SSBD) ||
> + static_cpu_has(X86_FEATURE_AMD_SSBD))
> hostval |= ssbd_tif_to_spec_ctrl(ti->flags);
>
> if (hostval != guestval) {
> @@ -533,9 +534,10 @@ static enum ssb_mitigation __init __ssb_select_mitigation(void)
> * Intel uses the SPEC CTRL MSR Bit(2) for this, while AMD may
> * use a completely different MSR and bit dependent on family.
> */
> - if (!static_cpu_has(X86_FEATURE_MSR_SPEC_CTRL))
> + if (!static_cpu_has(X86_FEATURE_SPEC_CTRL_SSBD) &&
> + !static_cpu_has(X86_FEATURE_AMD_SSBD)) {
> x86_amd_ssb_disable();
> - else {
> + } else {
> x86_spec_ctrl_base |= SPEC_CTRL_SSBD;
> x86_spec_ctrl_mask |= SPEC_CTRL_SSBD;
> wrmsrl(MSR_IA32_SPEC_CTRL, x86_spec_ctrl_base);
>

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