Re: [PATCH v2 03/10] xen/arm: vgic: implement helper functions for virq checks

[Leonid Komarianskyi <Leonid_Komarianskyi@xxxxxxxx>]

Hi Volodymyr,

Thank you for you comment.

On 21.08.25 18:46, Volodymyr Babchuk wrote:
> 
> Leonid Komarianskyi <Leonid_Komarianskyi@xxxxxxxx> writes:
> 
>> Introduced two new helper functions for vGIC: vgic_is_valid_irq and
>> vgic_is_shared_irq. The functions are similar to the newly introduced
>> gic_is_valid_irq and gic_is_shared_irq, but they verify whether a vIRQ
>> is available for a specific domain, while GIC-specific functions
>> validate INTIDs for the real GIC hardware. For example, the GIC may
>> support all 992 SPI lines, but the domain may use only some part of them
>> (e.g., 640), depending on the highest IRQ number defined in the domain
>> configuration. Therefore, for vGIC-related code and checks, the
>> appropriate functions should be used. Also, updated the appropriate
>> checks to use these new helper functions.
>>
>> The purpose of introducing new helper functions for vGIC is essentially
>> the same as for GIC: to avoid potential confusion with GIC-related
>> checks and to consolidate similar code into separate functions, which
>> can be more easily extended by additional conditions, e.g., when
>> implementing extended SPI interrupts.
>>
>> Only the validation change in vgic_inject_irq may affect existing
>> functionality, as it currently checks whether the vIRQ is less than or
>> equal to vgic_num_irqs. Since IRQ indexes start from 0 (where 32 is the
>> first SPI), the check should behave consistently with similar logic in
>> other places and should check if the vIRQ number is less than
>> vgic_num_irqs. The remaining changes, which replace open-coded checks
>> with the use of these new helper functions, do not introduce any
>> functional changes, as the helper functions follow the current vIRQ
>> index verification logic.
>>
>> Signed-off-by: Leonid Komarianskyi <leonid_komarianskyi@xxxxxxxx>
>>
>> ---
>> Changes in V2:
>> - introduced this patch
>> ---
>>   xen/arch/arm/gic.c              |  3 +--
>>   xen/arch/arm/include/asm/vgic.h |  7 +++++++
>>   xen/arch/arm/irq.c              |  4 ++--
>>   xen/arch/arm/vgic.c             | 10 ++++++++--
>>   4 files changed, 18 insertions(+), 6 deletions(-)
>>
>> diff --git a/xen/arch/arm/gic.c b/xen/arch/arm/gic.c
>> index eb0346a898..47fccf21d8 100644
>> --- a/xen/arch/arm/gic.c
>> +++ b/xen/arch/arm/gic.c
>> @@ -133,8 +133,7 @@ int gic_route_irq_to_guest(struct domain *d, unsigned 
>> int virq,
>>   
>>       ASSERT(spin_is_locked(&desc->lock));
>>       /* Caller has already checked that the IRQ is an SPI */
>> -    ASSERT(virq >= 32);
>> -    ASSERT(virq < vgic_num_irqs(d));
>> +    ASSERT(vgic_is_shared_irq(d, virq));
>>       ASSERT(!is_lpi(virq));
>>   
>>       ret = vgic_connect_hw_irq(d, NULL, virq, desc, true);
>> diff --git a/xen/arch/arm/include/asm/vgic.h 
>> b/xen/arch/arm/include/asm/vgic.h
>> index 35c0c6a8b0..45201f4ca5 100644
>> --- a/xen/arch/arm/include/asm/vgic.h
>> +++ b/xen/arch/arm/include/asm/vgic.h
>> @@ -335,6 +335,13 @@ extern void vgic_check_inflight_irqs_pending(struct 
>> vcpu *v,
>>   /* Default number of vGIC SPIs. 32 are substracted to cover local IRQs. */
>>   #define VGIC_DEF_NR_SPIS (min(gic_number_lines(), VGIC_MAX_IRQS) - 32)
>>   
>> +extern bool vgic_is_valid_irq(struct domain *d, unsigned int virq);
>> +
>> +static inline bool vgic_is_shared_irq(struct domain *d, unsigned int virq)
>> +{
>> +    return (virq >= NR_LOCAL_IRQS && vgic_is_valid_irq(d, virq));
>> +}
>> +
>>   /*
>>    * Allocate a guest VIRQ
>>    *  - spi == 0 => allocate a PPI. It will be the same on every vCPU
>> diff --git a/xen/arch/arm/irq.c b/xen/arch/arm/irq.c
>> index 12c70d02cc..50e57aaea7 100644
>> --- a/xen/arch/arm/irq.c
>> +++ b/xen/arch/arm/irq.c
>> @@ -442,7 +442,7 @@ int route_irq_to_guest(struct domain *d, unsigned int 
>> virq,
>>       unsigned long flags;
>>       int retval = 0;
>>   
>> -    if ( virq >= vgic_num_irqs(d) )
>> +    if ( !vgic_is_valid_irq(d, virq) )
>>       {
>>           printk(XENLOG_G_ERR
>>                  "the vIRQ number %u is too high for domain %u (max = %u)\n",
>> @@ -560,7 +560,7 @@ int release_guest_irq(struct domain *d, unsigned int 
>> virq)
>>       int ret;
>>   
>>       /* Only SPIs are supported */
>> -    if ( virq < NR_LOCAL_IRQS || virq >= vgic_num_irqs(d) )
>> +    if ( !vgic_is_shared_irq(d, virq) )
>>           return -EINVAL;
>>   
>>       desc = vgic_get_hw_irq_desc(d, NULL, virq);
>> diff --git a/xen/arch/arm/vgic.c b/xen/arch/arm/vgic.c
>> index c563ba93af..48fbaf56fb 100644
>> --- a/xen/arch/arm/vgic.c
>> +++ b/xen/arch/arm/vgic.c
>> @@ -24,6 +24,12 @@
>>   #include <asm/gic.h>
>>   #include <asm/vgic.h>
>>   
>> +
>> +bool vgic_is_valid_irq(struct domain *d, unsigned int virq)
> 
> I have the same comment as for the previous patch. This function
> completely ignores LPIs presence, while you can't argue that LPIs as
> valid. Again, function callers are expecting this behavior, so this is
> fine, but function name should better reflect its behavior.
> 
> [...]
> 

Would it be okay to rename these functions as proposed in the previous 
patch discussion:
vgic_is_valid_irq -> vgic_is_valid_line
vgic_is_shared_irq -> vgic_is_spi?

Or, in the case of vgic, is it not a good idea to use the "line" suffix 
because vgic does not have physical interrupt lines? Would it be better 
to rename it to vgic_is_valid_non_lpi instead?

Best regards,
Leonid