Re: [PATCH 1/2] arm: vgic: Add the ability to trigger MSIs from the Hypervisor

From: Julien Grall <julien@xen.org>
To: Mykyta Poturai <Mykyta_Poturai@epam.com>,
	"xen-devel@lists.xenproject.org" <xen-devel@lists.xenproject.org>
Cc: Stefano Stabellini <sstabellini@kernel.org>,
	Bertrand Marquis <bertrand.marquis@arm.com>,
	Michal Orzel <michal.orzel@amd.com>,
	Volodymyr Babchuk <Volodymyr_Babchuk@epam.com>
Subject: Re: [PATCH 1/2] arm: vgic: Add the ability to trigger MSIs from the Hypervisor
Date: Wed, 24 Jan 2024 11:41:39 +0000	[thread overview]
Message-ID: <56da4008-f0a5-437f-b3ff-50220ea50c81@xen.org> (raw)
In-Reply-To: <e109a4092d80a825256d26a8e56dbb5a2ae6d04e.1705066642.git.mykyta_poturai@epam.com>

Hi,

On 14/01/2024 10:01, Mykyta Poturai wrote:
> Add the vgic_its_trigger_msi() function to the vgic interface. This
> function allows to inject MSIs from the Hypervisor to the guest.
> Which is useful for userspace PCI backend drivers.
> 
> Signed-off-by: Mykyta Poturai <mykyta_poturai@epam.com>
> ---
>   xen/arch/arm/include/asm/vgic.h | 11 +++++++++++
>   xen/arch/arm/vgic-v3-its.c      | 35 +++++++++++++++++++++++++++++++++
>   2 files changed, 46 insertions(+)
> 
> diff --git a/xen/arch/arm/include/asm/vgic.h b/xen/arch/arm/include/asm/vgic.h
> index 922779ce14..4695743848 100644
> --- a/xen/arch/arm/include/asm/vgic.h
> +++ b/xen/arch/arm/include/asm/vgic.h
> @@ -317,6 +317,17 @@ extern bool vgic_migrate_irq(struct vcpu *old, struct vcpu *new, unsigned int ir
>   extern void vgic_check_inflight_irqs_pending(struct domain *d, struct vcpu *v,
>                                                unsigned int rank, uint32_t r);
>   
> +#ifdef CONFIG_HAS_ITS
> +int vgic_its_trigger_msi(struct domain *d, paddr_t doorbell_address,
> +                                u32 devid, u32 eventid);
> +#else
> +static inline int vgic_its_trigger_msi(struct domain *d, paddr_t doorbell_address,
> +                                u32 devid, u32 eventid)
> +{
> +    return -EOPNOTSUPP;
> +}
> +#endif /* CONFIG_HAS_ITS */
> +
>   #endif /* !CONFIG_NEW_VGIC */
>   
>   /*** Common VGIC functions used by Xen arch code ****/
> diff --git a/xen/arch/arm/vgic-v3-its.c b/xen/arch/arm/vgic-v3-its.c
> index 70b5aeb822..683a378f6e 100644
> --- a/xen/arch/arm/vgic-v3-its.c
> +++ b/xen/arch/arm/vgic-v3-its.c
> @@ -1484,6 +1484,41 @@ static int vgic_v3_its_init_virtual(struct domain *d, paddr_t guest_addr,
>       return 0;
>   }
>   
> +int vgic_its_trigger_msi(struct domain *d, paddr_t doorbell_address,
> +                                u32 devid, u32 eventid)
> +{
> +    struct vcpu *vcpu;
> +    struct virt_its *pos, *temp;
> +    struct virt_its *its = NULL;
> +    uint32_t vlpi;
> +    bool ret;
> +
> +    list_for_each_entry_safe( pos, temp, &d->arch.vgic.vits_list, vits_list )
> +    {
> +        if ( pos->doorbell_address == doorbell_address )
> +        {
> +            its = pos;
> +            break;
> +        }
> +    }
> +
> +    if ( !its )
> +        return -EINVAL;
> +
> +    spin_lock(&its->its_lock);
> +    ret = read_itte(its, devid, eventid, &vcpu, &vlpi);
> +    spin_unlock(&its->its_lock);
> +    if ( !ret )
> +        return -1;
> +
> +    if ( vlpi == INVALID_LPI )
> +        return -1;

Reading the code, I think you want to use get_event_pending_irq(). This 
will return the associated pending_irq. Then you can...

> +
> +    vgic_vcpu_inject_lpi(its->d, vlpi);

... open-code vgic_vcpu_inject_lpi(). This would avoid access the guest 
memory (done by read_itte) and reduce to just one lookup (today you are 
doing two: read_itte() and irq_to_pending()).

Cheers,

-- 
Julien Grall