Re: [Xen-devel] [XEN PATCH for-4.13 v2 9/9] libxl/xl: Overhaul passthrough setting logic

From: Julien Grall <julien.grall@arm.com>
To: Andrew Cooper <andrew.cooper3@citrix.com>,
	Ian Jackson <ian.jackson@eu.citrix.com>,
	xen-devel@lists.xenproject.org
Cc: Anthony PERARD <anthony.perard@citrix.com>,
	Paul Durrant <pdurrant@gmail.com>, Wei Liu <wl@xen.org>,
	Jan Beulich <jbeulich@suse.com>
Subject: Re: [Xen-devel] [XEN PATCH for-4.13 v2 9/9] libxl/xl: Overhaul passthrough setting logic
Date: Fri, 11 Oct 2019 12:00:46 +0100	[thread overview]
Message-ID: <55f7b367-a593-5585-ffd1-7034f045b9a9@arm.com> (raw)
In-Reply-To: <17defd97-e6b8-761e-0bd8-0aa0a2de7bed@citrix.com>

Hi,

On 11/10/2019 10:47, Andrew Cooper wrote:
> On 10/10/2019 16:11, Ian Jackson wrote:
>> diff --git a/tools/libxl/libxl_create.c b/tools/libxl/libxl_create.c
>> index 69971c97b6..fccb6a6271 100644
>> --- a/tools/libxl/libxl_create.c
>> +++ b/tools/libxl/libxl_create.c
>> @@ -968,6 +957,50 @@ int libxl__domain_config_setdefault(libxl__gc *gc,
>>           goto error_out;
>>       }
>>   
>> +    bool need_pt = d_config->num_pcidevs || d_config->num_dtdevs;
>> +    if (c_info->passthrough == LIBXL_PASSTHROUGH_UNKNOWN) {
>> +        c_info->passthrough = need_pt
>> +            ? LIBXL_PASSTHROUGH_ENABLED : LIBXL_PASSTHROUGH_DISABLED;
>> +    }
>> +
>> +    bool iommu_enabled = physinfo.cap_hvm_directio;
>> +    if (c_info->passthrough != LIBXL_PASSTHROUGH_DISABLED && !iommu_enabled) {
>> +        LOGD(ERROR, domid,
>> +             "ERROR: passthrough not supported on this platform\n");
>> +        ret = ERROR_INVAL;
>> +        goto error_out;
>> +    }
>> +
>> +    if (c_info->passthrough == LIBXL_PASSTHROUGH_DISABLED && need_pt) {
>> +        LOGD(ERROR, domid,
>> +             "passthrough disabled but devices are specified");
> 
> This is the only log message which isn't prefixed with ERROR:
> 
>> +        ret = ERROR_INVAL;
>> +        goto error_out;
>> +    }
>> +
>> +    const char *whynot_pt_share =
>> +        c_info->type == LIBXL_DOMAIN_TYPE_PV ? "not valid for PV domain" :
>> +        !physinfo.cap_iommu_hap_pt_share ? "not supported on this platform" :
>> +        NULL;
> 
> This is a little more complicated.
> 
> For ARM, doesn't libxl treat guests as PV, or has that been fixed now?

libxl treats Arm guest as PVH now. Note that we seamlessly convert PV to PVH in 
libxl__arch_domain_{build, create}_info_setdefault().

So as long as this is called after any of those calls, then we should be fine.

> ARM's only passthrough mode is PT_SHARE.

Correct.

Cheers,

-- 
Julien Grall

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