linux-kernel - Re: [PATCH v1 2/8] x86/xen: simplify xen_oldmem_pfn_is

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Message-ID: <e9a230f9-85cb-d4c1-8027-508b7c344d94@redhat.com>
Date:   Wed, 29 Sep 2021 11:03:09 +0200
From:   David Hildenbrand <david@...hat.com>
To:     Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        linux-kernel@...r.kernel.org
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>, Juergen Gross <jgross@...e.com>,
        Stefano Stabellini <sstabellini@...nel.org>,
        "Michael S. Tsirkin" <mst@...hat.com>,
        Jason Wang <jasowang@...hat.com>,
        Dave Young <dyoung@...hat.com>, Baoquan He <bhe@...hat.com>,
        Vivek Goyal <vgoyal@...hat.com>,
        Michal Hocko <mhocko@...e.com>,
        Oscar Salvador <osalvador@...e.de>,
        Mike Rapoport <rppt@...nel.org>,
        "Rafael J. Wysocki" <rafael.j.wysocki@...el.com>, x86@...nel.org,
        xen-devel@...ts.xenproject.org,
        virtualization@...ts.linux-foundation.org,
        kexec@...ts.infradead.org, linux-fsdevel@...r.kernel.org,
        linux-mm@...ck.org
Subject: Re: [PATCH v1 2/8] x86/xen: simplify xen_oldmem_pfn_is_ram()

On 29.09.21 10:45, David Hildenbrand wrote:
>>
>> How about
>>
>>       return a.mem_type != HVMMEM_mmio_dm;
>>
> 
> Ha, how could I have missed that :)
> 
>>
>> Result should be promoted to int and this has added benefit of not requiring changes in patch 4.
>>
> 
> Can we go one step further and do
> 
> 
> @@ -20,24 +20,11 @@ static int xen_oldmem_pfn_is_ram(unsigned long pfn)
>           struct xen_hvm_get_mem_type a = {
>                   .domid = DOMID_SELF,
>                   .pfn = pfn,
> +               .mem_type = HVMMEM_ram_rw,
>           };
> -       int ram;
>    
> -       if (HYPERVISOR_hvm_op(HVMOP_get_mem_type, &a))
> -               return -ENXIO;
> -
> -       switch (a.mem_type) {
> -       case HVMMEM_mmio_dm:
> -               ram = 0;
> -               break;
> -       case HVMMEM_ram_rw:
> -       case HVMMEM_ram_ro:
> -       default:
> -               ram = 1;
> -               break;
> -       }
> -
> -       return ram;
> +       HYPERVISOR_hvm_op(HVMOP_get_mem_type, &a);
> +       return a.mem_type != HVMMEM_mmio_dm;
>    }
>    #endif
> 
> 
> Assuming that if HYPERVISOR_hvm_op() fails that
> .mem_type is not set to HVMMEM_mmio_dm.
> 

Okay we can't, due to "__must_check" ...

-- 
Thanks,

David / dhildenb