linux-kernel - Re: [PATCH v2] x86/xen: Add support for HVMOP_set_evtchn_upcall

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Date:   Tue, 26 Jul 2022 19:31:33 -0400
From:   Boris Ostrovsky <boris.ostrovsky@...cle.com>
To:     Jane Malalane <jane.malalane@...rix.com>,
        LKML <linux-kernel@...r.kernel.org>
Cc:     Juergen Gross <jgross@...e.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
        "H. Peter Anvin" <hpa@...or.com>,
        Stefano Stabellini <sstabellini@...nel.org>,
        Oleksandr Tyshchenko <oleksandr_tyshchenko@...m.com>,
        Maximilian Heyne <mheyne@...zon.de>,
        Jan Beulich <jbeulich@...e.com>,
        Colin Ian King <colin.king@...el.com>,
        xen-devel@...ts.xenproject.org
Subject: Re: [PATCH v2] x86/xen: Add support for
 HVMOP_set_evtchn_upcall_vector


On 7/26/22 8:56 AM, Jane Malalane wrote:
>   
> +/* Setup per-vCPU vector-type callbacks and trick toolstack to think
> + * we are enlightened. If this setup is unavailable, fallback to the
> + * global vector-type callback. */


Comment style.


> +static __init void xen_init_setup_upcall_vector(void)
> +{
> +	unsigned int cpu = 0;


Unnecessary variable.


> +
> +	if (!xen_have_vector_callback)
> +		return;
> +
> +	if ((cpuid_eax(xen_cpuid_base() + 4) & XEN_HVM_CPUID_UPCALL_VECTOR) &&
> +	    !xen_set_upcall_vector(cpu) && !xen_set_callback_via(1))
> +		xen_percpu_upcall = true;
> +	else if (xen_feature(XENFEAT_hvm_callback_vector))
> +		xen_setup_callback_vector();
> +	else
> +		xen_have_vector_callback = false;
> +}
> +
> +int xen_set_upcall_vector(unsigned int cpu)
> +{
> +	int rc;
> +	xen_hvm_evtchn_upcall_vector_t op = {
> +		.vector = HYPERVISOR_CALLBACK_VECTOR,
> +		.vcpu = per_cpu(xen_vcpu_id, cpu),
> +	};
> +
> +	rc = HYPERVISOR_hvm_op(HVMOP_set_evtchn_upcall_vector, &op);
> +	if (rc)
> +		return rc;
> +
> +	if (!cpu)


A comment (e.g. "Let toolstack know that we are enlightened." or something along these lines) would be useful here.


-boris


> +		rc = xen_set_callback_via(1);
> +