From 6b8e288f49570ee2ba15a2a07c2ebf7ad2210422 Mon Sep 17 00:00:00 2001 From: He Rongguang Date: Mon, 4 Mar 2024 14:14:06 +0800 Subject: cpuidle: ACPI/intel: fix MWAIT hint target C-state computation According to x86 spec ([1] and [2]), MWAIT hint_address[7:4] plus 1 is the corresponding C-state, and 0xF means C0. ACPI C-state table usually only contains C1+, but nothing prevents ACPI firmware from presenting a C-state (maybe C1+) but using 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 valid C0 instead of C16, as per the specifications. Since ACPI firmware is out of Linux kernel scope, fix the kernel handling of 0xF ->(to) C0 in this situation. This is found when a tweaked ACPI C-state table is presented by Qemu to VM. Also modify the intel_idle case for 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 [ rjw: Subject and changelog edits, whitespace fixups ] Signed-off-by: Rafael J. Wysocki --- drivers/idle/intel_idle.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) (limited to 'drivers/idle') 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; -- cgit v1.2.3