[v2] x86/cstate: fix mwait hint target cstate calc

According to x86 spec ([1] and [2]), mwait hint_address[7:4] adds 1 is
the corresponding cstate, and 0xF means C0.

ACPI cstate table usually only contains C1+, but nothing prevents ACPI
firmware from presenting a cstate (maybe C1+) but using a mwait address C0
(i.e., 0xF in ACPI FFH MWAIT hint address). And if this is the case, Linux
erroneously treat this cstate as C16, while actually this should be legal
C0 state instead of C16, according to spec.

Since ACPI firmware is out of Linux kernel scope, fix kernel handling of
0xF ->(to) C0 in this situation. This is found when tweak ACPI cstate
table qemu presenting to VM.

Also fix intel_idle case by the way for kernel code consistency.

[1]. Intel SDM Vol 2, Table 4-11. MWAIT Hints
Register (EAX): "Value of 0 means C1; 1 means C2 and so on
Value of 01111B means C0".

[2]. AMD manual Vol 3, MWAIT: "The processor C-state is EAX[7:4]+1, so to
request C0 is to place the value F in EAX[7:4] and to request C1 is to
place the value 0 in EAX[7:4].".

Signed-off-by: He Rongguang <herongguang@linux.alibaba.com>
---
V1 -> V2: Amend commit message according to Rafael.

  arch/x86/kernel/acpi/cstate.c | 4 ++--
  drivers/idle/intel_idle.c     | 3 ++-
  2 files changed, 4 insertions(+), 3 deletions(-)


--
2.43.0

On Mon, Mar 4, 2024 at 7:14 AM He Rongguang
<herongguang@linux.alibaba.com> wrote:
>
> According to x86 spec ([1] and [2]), mwait hint_address[7:4] adds 1 is
> the corresponding cstate, and 0xF means C0.
>
> ACPI cstate table usually only contains C1+, but nothing prevents ACPI
> firmware from presenting a cstate (maybe C1+) but using a mwait address C0
> (i.e., 0xF in ACPI FFH MWAIT hint address). And if this is the case, Linux
> erroneously treat this cstate as C16, while actually this should be legal
> C0 state instead of C16, according to spec.
>
> Since ACPI firmware is out of Linux kernel scope, fix kernel handling of
> 0xF ->(to) C0 in this situation. This is found when tweak ACPI cstate
> table qemu presenting to VM.
>
> Also fix intel_idle case by the way for kernel code consistency.
>
> [1]. Intel SDM Vol 2, Table 4-11. MWAIT Hints
> Register (EAX): "Value of 0 means C1; 1 means C2 and so on
> Value of 01111B means C0".
>
> [2]. AMD manual Vol 3, MWAIT: "The processor C-state is EAX[7:4]+1, so to
> request C0 is to place the value F in EAX[7:4] and to request C1 is to
> place the value 0 in EAX[7:4].".
>
> Signed-off-by: He Rongguang <herongguang@linux.alibaba.com>
> ---
> V1 -> V2: Amend commit message according to Rafael.
>
>   arch/x86/kernel/acpi/cstate.c | 4 ++--
>   drivers/idle/intel_idle.c     | 3 ++-
>   2 files changed, 4 insertions(+), 3 deletions(-)
>
> diff --git a/arch/x86/kernel/acpi/cstate.c b/arch/x86/kernel/acpi/cstate.c
> index 401808b47af3..f3ffd0a3a012 100644
> --- a/arch/x86/kernel/acpi/cstate.c
> +++ b/arch/x86/kernel/acpi/cstate.c
> @@ -131,8 +131,8 @@ static long acpi_processor_ffh_cstate_probe_cpu(void
> *_cx)
>          cpuid(CPUID_MWAIT_LEAF, &eax, &ebx, &ecx, &edx);
>
>          /* Check whether this particular cx_type (in CST) is supported
> or not */
> -       cstate_type = ((cx->address >> MWAIT_SUBSTATE_SIZE) &
> -                       MWAIT_CSTATE_MASK) + 1;
> +       cstate_type = (((cx->address >> MWAIT_SUBSTATE_SIZE) &
> +                       MWAIT_CSTATE_MASK) + 1) & MWAIT_CSTATE_MASK;
>          edx_part = edx >> (cstate_type * MWAIT_SUBSTATE_SIZE);
>          num_cstate_subtype = edx_part & MWAIT_SUBSTATE_MASK;
>
> diff --git a/drivers/idle/intel_idle.c b/drivers/idle/intel_idle.c
> index bcf1198e8991..e486027f8b07 100644
> --- a/drivers/idle/intel_idle.c
> +++ b/drivers/idle/intel_idle.c
> @@ -1934,7 +1934,8 @@ static void __init spr_idle_state_table_update(void)
>
>   static bool __init intel_idle_verify_cstate(unsigned int mwait_hint)
>   {
> -       unsigned int mwait_cstate = MWAIT_HINT2CSTATE(mwait_hint) + 1;
> +       unsigned int mwait_cstate = (MWAIT_HINT2CSTATE(mwait_hint) + 1) &
> +                                       MWAIT_CSTATE_MASK;
>          unsigned int num_substates = (mwait_substates >> mwait_cstate *
> 4) &
>                                          MWAIT_SUBSTATE_MASK;
>
> --

Applied as 6.9 material with some edits in the subject and changelog.

Also, your email client mangles white space, so please consider using
a different one for sending patches.

Thanks!

在 2024/3/6 4:30, Rafael J. Wysocki 写道:


> Also, your email client mangles white space, so please consider using
> a different one for sending patches.
> 
> Thanks!

Ok, it turns out it is in Windows Terminal that copy will change tab to 
white space, I will pay attention to this from the moment, thanks for 
your reminder.