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Message-ID: <be31db14-9545-4d11-9392-458782e10b48@amd.com>
Date: Thu, 17 Apr 2025 17:30:13 +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, francescolavra.fl@...il.com
Subject: Re: [PATCH v4 06/18] x86/apic: Add update_vector callback for Secure
AVIC
On 4/17/2025 4:20 PM, Thomas Gleixner wrote:
> On Thu, Apr 17 2025 at 14:46, Neeraj Upadhyay wrote:
>> Add update_vector callback to set/clear ALLOWED_IRR field in
>> a vCPU's APIC backing page for external vectors. The ALLOWED_IRR
>> field indicates the interrupt vectors which the guest allows the
>> hypervisor to send (typically for emulated devices). Interrupt
>> vectors used exclusively by the guest itself and the vectors which
>> are not emulated by the hypervisor, such as IPI vectors, are part
>> of system vectors and are not set in the ALLOWED_IRR.
>
> Please structure changelogs properly in paragraphs:
>
> https://www.kernel.org/doc/html/latest/process/maintainer-tip.html#changelog
>
Ok
>> arch/x86/include/asm/apic.h | 9 +++++
>> arch/x86/kernel/apic/vector.c | 53 ++++++++++++++++++++++-------
>> arch/x86/kernel/apic/x2apic_savic.c | 35 +++++++++++++++++++
>
> And split this patch up into two:
>
> 1) Do the modifications in vector.c which is what the $Subject line
> says
>
> 2) Add the SAVIC specific bits
>
Ok
>> @@ -471,6 +473,12 @@ static __always_inline bool apic_id_valid(u32 apic_id)
>> return apic_id <= apic->max_apic_id;
>> }
>>
>> +static __always_inline void apic_update_vector(unsigned int cpu, unsigned int vector, bool set)
>> +{
>> + if (apic->update_vector)
>> + apic->update_vector(cpu, vector, set);
>> +}
>
> This is in the public header because it can?
>
apic_update_vector() is needed for some system vectors which are emulated/injected
by Hypervisor. Patch 8 calls it for lapic timer. HYPERVISOR_CALLBACK_VECTOR would need
it for hyperv. This patch series does not call apic_update_vector() for
HYPERVISOR_CALLBACK_VECTOR though.
Given that currently this callback is not used outside of apic code,
do I need to add it to arch/x86/kernel/apic/local.h or just remove it and use
conditional call in current callsites?
>> -static void apic_update_vector(struct irq_data *irqd, unsigned int newvec,
>> - unsigned int newcpu)
>> +static int irq_alloc_vector(const struct cpumask *dest, bool resvd, unsigned int *cpu)
>> +{
>> + int vector;
>> +
>> + vector = irq_matrix_alloc(vector_matrix, dest, resvd, cpu);
>
> int vector = irq_matrix_alloc(...);
>
Ok
>> +
>> + if (vector >= 0)
>> + apic_update_vector(*cpu, vector, true);
>> +
>> + return vector;
>> +}
>> +
>> +static int irq_alloc_managed_vector(unsigned int *cpu)
>> +{
>> + int vector;
>> +
>> + vector = irq_matrix_alloc_managed(vector_matrix, vector_searchmask, cpu);
>> +
>> + if (vector >= 0)
>> + apic_update_vector(*cpu, vector, true);
>> +
>> + return vector;
>> +}
>
> I completely fail to see the value of these two functions. Each of them
> has exactly _ONE_ call site and both sites invoke apic_update_vector()
Ok, this was done to associate apic->update_vector() calls with the
setup (irq_matrix_alloc()) and teardown (irq_matrix_free()) of vector,
which was my understanding from your suggestion here:
https://lore.kernel.org/lkml/87jz8i31dv.ffs@tglx/ . Given that there
is single callsite for each and vector_configure_legacy() calls
apic->update_vector() outside of alloc path, adding it to apic_update_irq_cfg(),
as you suggest handles all callers.
> when the allocation succeeded. Why can't you just do the obvious and
> leave the existing code alone and add
>
> if (apic->update_vector)
> apic->update_vector();
>
> into apic_update_vector()? But then you have another place where you
> need the update, which does not invoke apic_update_vector().
>
> Now if you look deeper, then you notice that all places which invoke
> apic_update_vector() invoke apic_update_irq_cfg(), which is also called
> at this other place, no?
>
Yes, makes sense. apic_update_irq_cfg() is called for MANAGED_IRQ_SHUTDOWN_VECTOR
also. I am not aware of the use case of that vector. Whethere it is an interrupt
which is injected by Hypervisor.
static void vector_assign_managed_shutdown(struct irq_data *irqd)
{
unsigned int cpu = cpumask_first(cpu_online_mask);
apic_update_irq_cfg(irqd, MANAGED_IRQ_SHUTDOWN_VECTOR, cpu);
}
>> +static void irq_free_vector(unsigned int cpu, unsigned int vector, bool managed)
>> +{
>> + apic_update_vector(cpu, vector, false);
>> + irq_matrix_free(vector_matrix, cpu, vector, managed);
>> +}
>
> This one makes sense, but please name it: apic_free_vector()
>
Ok
> Something like the uncompiled below, no?
>
Ok, makes sense. Looks good.
- Neeraj
> Thanks,
>
> tglx
> ---
> --- a/arch/x86/kernel/apic/vector.c
> +++ b/arch/x86/kernel/apic/vector.c
> @@ -134,9 +134,19 @@ static void apic_update_irq_cfg(struct i
>
> apicd->hw_irq_cfg.vector = vector;
> apicd->hw_irq_cfg.dest_apicid = apic->calc_dest_apicid(cpu);
> +
> + if (apic->update_vector)
> + apic->update_vector(cpu, vector, true);
> +
> irq_data_update_effective_affinity(irqd, cpumask_of(cpu));
> - trace_vector_config(irqd->irq, vector, cpu,
> - apicd->hw_irq_cfg.dest_apicid);
> + trace_vector_config(irqd->irq, vector, cpu, apicd->hw_irq_cfg.dest_apicid);
> +}
> +
> +static void apic_free_vector(unsigned int cpu, unsigned int vector, bool managed)
> +{
> + if (apic->update_vector)
> + apic->update_vector(cpu, vector, false);
> + irq_matrix_free(vector_matrix, cpu, vector, managed);
> }
>
> static void apic_update_vector(struct irq_data *irqd, unsigned int newvec,
> @@ -174,8 +184,7 @@ static void apic_update_vector(struct ir
> apicd->prev_cpu = apicd->cpu;
> WARN_ON_ONCE(apicd->cpu == newcpu);
> } else {
> - irq_matrix_free(vector_matrix, apicd->cpu, apicd->vector,
> - managed);
> + apic_free_vector(apicd->cpu, apicd->vector, managed);
> }
>
> setnew:
> @@ -183,6 +192,7 @@ static void apic_update_vector(struct ir
> apicd->cpu = newcpu;
> BUG_ON(!IS_ERR_OR_NULL(per_cpu(vector_irq, newcpu)[newvec]));
> per_cpu(vector_irq, newcpu)[newvec] = desc;
> + apic_update_irq_cfg(irqd, newvec, newcpu);
> }
>
> static void vector_assign_managed_shutdown(struct irq_data *irqd)
> @@ -261,8 +271,6 @@ assign_vector_locked(struct irq_data *ir
> if (vector < 0)
> return vector;
> apic_update_vector(irqd, vector, cpu);
> - apic_update_irq_cfg(irqd, vector, cpu);
> -
> return 0;
> }
>
> @@ -338,7 +346,6 @@ assign_managed_vector(struct irq_data *i
> if (vector < 0)
> return vector;
> apic_update_vector(irqd, vector, cpu);
> - apic_update_irq_cfg(irqd, vector, cpu);
> return 0;
> }
>
> @@ -357,7 +364,7 @@ static void clear_irq_vector(struct irq_
> apicd->prev_cpu);
>
> per_cpu(vector_irq, apicd->cpu)[vector] = VECTOR_SHUTDOWN;
> - irq_matrix_free(vector_matrix, apicd->cpu, vector, managed);
> + apic_free_vector(apicd->cpu, vector, managed);
> apicd->vector = 0;
>
> /* Clean up move in progress */
> @@ -366,7 +373,7 @@ static void clear_irq_vector(struct irq_
> return;
>
> per_cpu(vector_irq, apicd->prev_cpu)[vector] = VECTOR_SHUTDOWN;
> - irq_matrix_free(vector_matrix, apicd->prev_cpu, vector, managed);
> + apic_free_vector(apicd->prev_cpu, vector, managed);
> apicd->prev_vector = 0;
> apicd->move_in_progress = 0;
> hlist_del_init(&apicd->clist);
> @@ -905,7 +912,7 @@ static void free_moved_vector(struct api
> * affinity mask comes online.
> */
> trace_vector_free_moved(apicd->irq, cpu, vector, managed);
> - irq_matrix_free(vector_matrix, cpu, vector, managed);
> + apic_free_vector(cpu, vector, managed);
> per_cpu(vector_irq, cpu)[vector] = VECTOR_UNUSED;
> hlist_del_init(&apicd->clist);
> apicd->prev_vector = 0;
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