On Wed, May 22, 2019 at 10:17:45PM +0000, Frank van der Linden wrote:
> For F17h AMD CPUs, the CPB capability is forcibly set, because some
> versions of that chip incorrectly report that they do not have it.
>
> However, a hypervisor may filter out the CPB capability, for good
> reasons. For example, KVM currently does not emulate setting the CPB
> bit in MSR_K7_HWCR, and unchecked MSR access errors will be thrown
> when trying to set it as a guest:
>
> unchecked MSR access error: WRMSR to 0xc0010015 (tried to write
> 0x0000000001000011) at rIP: 0xffffffff890638f4
> (native_write_msr+0x4/0x20)
>
> Call Trace:
> boost_set_msr+0x50/0x80 [acpi_cpufreq]
> cpuhp_invoke_callback+0x86/0x560
> sort_range+0x20/0x20
> cpuhp_thread_fun+0xb0/0x110
> smpboot_thread_fn+0xef/0x160
> kthread+0x113/0x130
> kthread_create_worker_on_cpu+0x70/0x70
> ret_from_fork+0x35/0x40
>
> To avoid this issue, don't forcibly set the CPB capability for a CPU
> when running under a hypervisor.
>
> Signed-off-by: Frank van der Linden <fllin...@amazon.com>
> Fixes: 0237199186e7 ("x86/CPU/AMD: Set the CPB bit unconditionally on F17h")
> ---
> arch/x86/kernel/cpu/amd.c | 7 +++++--
> 1 file changed, 5 insertions(+), 2 deletions(-)
>
> diff --git a/arch/x86/kernel/cpu/amd.c b/arch/x86/kernel/cpu/amd.c
> index fb6a64bd765f..ee4d79fa1b19 100644
> --- a/arch/x86/kernel/cpu/amd.c
> +++ b/arch/x86/kernel/cpu/amd.c
> @@ -823,8 +823,11 @@ static void init_amd_zn(struct cpuinfo_x86 *c)
> {
> set_cpu_cap(c, X86_FEATURE_ZEN);
>
> - /* Fix erratum 1076: CPB feature bit not being set in CPUID. */
> - if (!cpu_has(c, X86_FEATURE_CPB))
> + /*
> + * Fix erratum 1076: CPB feature bit not being set in CPUID.
> + * Always set it, except when running under a hypervisor.
> + */
> + if (!cpu_has(c, X86_FEATURE_HYPERVISOR) && !cpu_has(c, X86_FEATURE_CPB))
> set_cpu_cap(c, X86_FEATURE_CPB);
> }
I guess...
Acked-by: Borislav Petkov <b...@suse.de>
Btw, it has come up before whether it would be additionally prudent
to replace those *msr calls with their *msr_safe counterparts, in
boost_set_msr() and also check *msr_safe() retvals and exit early there.
Just in case and exactly because of virt.
--
Regards/Gruss,
Boris.
ECO tip #101: Trim your mails when you reply. Srsly.
