linux-kernel - Re: [RFC v2 01/17] x86/apic: Add new driver for Secure AVIC

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Message-ID: <a8320094-8002-49e3-881c-c5939002675c@amd.com>
Date: Fri, 21 Mar 2025 18:55:24 +0530
From: Neeraj Upadhyay <Neeraj.Upadhyay@....com>
To: Thomas Gleixner <tglx@...utronix.de>, linux-kernel@...r.kernel.org
Cc: bp@...en8.de, mingo@...hat.com, dave.hansen@...ux.intel.com,
 Thomas.Lendacky@....com, nikunj@....com, Santosh.Shukla@....com,
 Vasant.Hegde@....com, Suravee.Suthikulpanit@....com, David.Kaplan@....com,
 x86@...nel.org, hpa@...or.com, peterz@...radead.org, seanjc@...gle.com,
 pbonzini@...hat.com, kvm@...r.kernel.org, kirill.shutemov@...ux.intel.com,
 huibo.wang@....com, naveen.rao@....com
Subject: Re: [RFC v2 01/17] x86/apic: Add new driver for Secure AVIC



On 3/21/2025 6:23 PM, Thomas Gleixner wrote:
> On Wed, Feb 26 2025 at 14:35, Neeraj Upadhyay wrote:
>> +static void x2apic_savic_send_IPI(int cpu, int vector)
>> +{
>> +	u32 dest = per_cpu(x86_cpu_to_apicid, cpu);
>> +
>> +	/* x2apic MSRs are special and need a special fence: */
>> +	weak_wrmsr_fence();
>> +	__x2apic_send_IPI_dest(dest, vector, APIC_DEST_PHYSICAL);
>> +}
>> +
>> +static void
>> +__send_IPI_mask(const struct cpumask *mask, int vector, int apic_dest)
>> +{
>> +	unsigned long query_cpu;
>> +	unsigned long this_cpu;
>> +	unsigned long flags;
>> +
>> +	/* x2apic MSRs are special and need a special fence: */
>> +	weak_wrmsr_fence();
>> +
>> +	local_irq_save(flags);
>> +
>> +	this_cpu = smp_processor_id();
>> +	for_each_cpu(query_cpu, mask) {
>> +		if (apic_dest == APIC_DEST_ALLBUT && this_cpu == query_cpu)
>> +			continue;
>> +		__x2apic_send_IPI_dest(per_cpu(x86_cpu_to_apicid, query_cpu),
>> +				       vector, APIC_DEST_PHYSICAL);
>> +	}
>> +	local_irq_restore(flags);
>> +}
>> +
>> +static void x2apic_savic_send_IPI_mask(const struct cpumask *mask, int vector)
>> +{
>> +	__send_IPI_mask(mask, vector, APIC_DEST_ALLINC);
>> +}
>> +
>> +static void x2apic_savic_send_IPI_mask_allbutself(const struct cpumask *mask, int vector)
>> +{
>> +	__send_IPI_mask(mask, vector, APIC_DEST_ALLBUT);
>> +}
> 
> The above are identical copies (aside of the names) of the functions in
> x2apic_phys.c.
> 
> Why can't this simply share the code ?
> 

In patch "06/17 x86/apic: Add support to send IPI for Secure AVIC",
__send_IPI_mask() becomes different. It is modified to call functions which do
Secure AVIC specific handling - weak_wrmsr_fence() is not required and instead
of wrmsr, APIC_IRR is updated in the APIC backing page memory. 


- Neeraj

> Thanks,
> 
>         tglx