netdev - Re: [PATCH 03/12] x86/xen: Introduce new function to map HYPERVISOR_shared

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Date:   Sat, 30 May 2020 19:02:01 -0400
From:   Boris Ostrovsky <boris.ostrovsky@...cle.com>
To:     Anchal Agarwal <anchalag@...zon.com>, tglx@...utronix.de,
        mingo@...hat.com, bp@...en8.de, hpa@...or.com, x86@...nel.org,
        jgross@...e.com, linux-pm@...r.kernel.org, linux-mm@...ck.org,
        kamatam@...zon.com, sstabellini@...nel.org, konrad.wilk@...cle.com,
        roger.pau@...rix.com, axboe@...nel.dk, davem@...emloft.net,
        rjw@...ysocki.net, len.brown@...el.com, pavel@....cz,
        peterz@...radead.org, eduval@...zon.com, sblbir@...zon.com,
        xen-devel@...ts.xenproject.org, vkuznets@...hat.com,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        dwmw@...zon.co.uk, benh@...nel.crashing.org
Subject: Re: [PATCH 03/12] x86/xen: Introduce new function to map
 HYPERVISOR_shared_info on Resume

On 5/19/20 7:25 PM, Anchal Agarwal wrote:
> Introduce a small function which re-uses shared page's PA allocated
> during guest initialization time in reserve_shared_info() and not
> allocate new page during resume flow.
> It also  does the mapping of shared_info_page by calling
> xen_hvm_init_shared_info() to use the function.
>
> Signed-off-by: Anchal Agarwal <anchalag@...zon.com>
> ---
>  arch/x86/xen/enlighten_hvm.c | 7 +++++++
>  arch/x86/xen/xen-ops.h       | 1 +
>  2 files changed, 8 insertions(+)
>
> diff --git a/arch/x86/xen/enlighten_hvm.c b/arch/x86/xen/enlighten_hvm.c
> index e138f7de52d2..75b1ec7a0fcd 100644
> --- a/arch/x86/xen/enlighten_hvm.c
> +++ b/arch/x86/xen/enlighten_hvm.c
> @@ -27,6 +27,13 @@
>  
>  static unsigned long shared_info_pfn;
>  
> +void xen_hvm_map_shared_info(void)
> +{
> +	xen_hvm_init_shared_info();
> +	if (shared_info_pfn)
> +		HYPERVISOR_shared_info = __va(PFN_PHYS(shared_info_pfn));
> +}
> +


AFAICT it is only called once so I don't see a need for new routine.


And is it possible for shared_info_pfn to be NULL in resume path (which
is where this is called)?


-boris