Re: [PATCH v5 2/2] KVM: VMX: Cap VMX preemption timer to work around Intel erratum

[Binbin Wu <binbin.wu@linux.intel.com>]

On 7/25/2026 7:49 AM, Jim Mattson wrote:
> Due to a widespread Intel erratum (e.g. EMR158), programming the
> VMX-preemption timer with certain large values may cause the timer to
> expire earlier than expected.  The recommended workaround is to cap the
> VMX-preemption timer value to strictly less than 2^25 * CPUID.15H:EBX[31:0]
> / CPUID.15H:EAX[31:0].
> 
> Calculate preemption_timer_limit during hardware setup based on CPUID 15H
> when available, and return -ERANGE in vmx_set_hv_timer() if the shifted
> delta_tsc reaches or exceeds preemption_timer_limit.
> 
> Use preemption_timer_limit - 1 instead of 0xffffffff when soft-disabling
> the timer and when checking the timer frequency limit in hardware setup.
> 
> Reported-by: Sean Christopherson <seanjc@google.com>
> Closes: https://lore.kernel.org/all/Zn9X0yFxZi_Mrlnt@google.com/
> Suggested-by: Chao Gao <chao.gao@intel.com>
> Assisted-by: Gemini:Gemini-Next
> Reviewed-by: Chao Gao <chao.gao@intel.com>
> Signed-off-by: Jim Mattson <jmattson@google.com>

Reviewed-by: Binbin Wu <binbin.wu@linux.intel.com>