[PATCH 3/4] Revert part of "x86/mwait-idle: disable IBRS during long idle"

Most of the patch (handling of CPUIDLE_FLAG_IBRS) is fine, but the adjustements to mwait_idle() are not. spec_ctrl_{enter,exit}_idle() do more than just alter MSR_SPEC_CTRL.IBRS. The VERW and RSB stuff are **unsafe** to omit. The only reason this doesn't need an XSA is because no changes were ma

Re: [PATCH 3/4] Revert part of "x86/mwait-idle: disable IBRS during long idle"

On 25.06.2025 15:01, Andrew Cooper wrote: > On 25/06/2025 10:58 am, Jan Beulich wrote: >> On 24.06.2025 18:39, Andrew Cooper wrote: >>> Most of the patch (handling of CPUIDLE_FLAG_IBRS) is fine, but the >>> adjustements to mwait_idle() are not. >>> >>> spec_ctrl_{enter,exit}_idle() do more than jus

Re: [PATCH 3/4] Revert part of "x86/mwait-idle: disable IBRS during long idle"

On 25/06/2025 10:58 am, Jan Beulich wrote: > On 24.06.2025 18:39, Andrew Cooper wrote: >> Most of the patch (handling of CPUIDLE_FLAG_IBRS) is fine, but the >> adjustements to mwait_idle() are not. >> >> spec_ctrl_{enter,exit}_idle() do more than just alter MSR_SPEC_CTRL.IBRS. >> The >> VERW and

Re: [PATCH 3/4] Revert part of "x86/mwait-idle: disable IBRS during long idle"

On 24.06.2025 18:39, Andrew Cooper wrote: > Most of the patch (handling of CPUIDLE_FLAG_IBRS) is fine, but the > adjustements to mwait_idle() are not. > > spec_ctrl_{enter,exit}_idle() do more than just alter MSR_SPEC_CTRL.IBRS. The > VERW and RSB stuff are **unsafe** to omit. > > The only reaso