Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
Subject: Re: [PATCH v1 2/8] x86/xen: simplify xen_oldmem_pfn_is_ram()
From:   David Hildenbrand <david@redhat.com>
To:     Boris Ostrovsky <boris.ostrovsky@oracle.com>,
        linux-kernel@vger.kernel.org
Cc:     Andrew Morton <akpm@linux-foundation.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
        "H. Peter Anvin" <hpa@zytor.com>, Juergen Gross <jgross@suse.com>,
        Stefano Stabellini <sstabellini@kernel.org>,
        "Michael S. Tsirkin" <mst@redhat.com>,
        Jason Wang <jasowang@redhat.com>,
        Dave Young <dyoung@redhat.com>, Baoquan He <bhe@redhat.com>,
        Vivek Goyal <vgoyal@redhat.com>,
        Michal Hocko <mhocko@suse.com>,
        Oscar Salvador <osalvador@suse.de>,
        Mike Rapoport <rppt@kernel.org>,
        "Rafael J. Wysocki" <rafael.j.wysocki@intel.com>, x86@kernel.org,
        xen-devel@lists.xenproject.org,
        virtualization@lists.linux-foundation.org,
        kexec@lists.infradead.org, linux-fsdevel@vger.kernel.org,
        linux-mm@kvack.org
References: <20210928182258.12451-1-david@redhat.com>
 <20210928182258.12451-3-david@redhat.com>
 <4ab2f8c2-c3d5-30b3-a670-a8b38e218b6e@oracle.com>
 <bfe72f46-9a0d-1a87-64bd-4b03999edd1e@redhat.com>
Organization: Red Hat
Message-ID: <e9a230f9-85cb-d4c1-8027-508b7c344d94@redhat.com>
Date:   Wed, 29 Sep 2021 11:03:09 +0200
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101
 Thunderbird/78.11.0
MIME-Version: 1.0
In-Reply-To: <bfe72f46-9a0d-1a87-64bd-4b03999edd1e@redhat.com>
Content-Type: text/plain; charset=utf-8; format=flowed
Content-Language: en-US
Content-Transfer-Encoding: 8bit
Precedence: bulk

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