Re: [PATCH] public: there's no MMUEXT_SET_FOREIGNDOM

From: Julien Grall <julien.grall@arm.com>
To: Jan Beulich <JBeulich@suse.com>,
	xen-devel <xen-devel@lists.xenproject.org>
Cc: Stefano Stabellini <sstabellini@kernel.org>,
	Wei Liu <wei.liu2@citrix.com>,
	George Dunlap <George.Dunlap@eu.citrix.com>,
	Andrew Cooper <andrew.cooper3@citrix.com>,
	Ian Jackson <Ian.Jackson@eu.citrix.com>, Tim Deegan <tim@xen.org>
Subject: Re: [PATCH] public: there's no MMUEXT_SET_FOREIGNDOM
Date: Fri, 9 Jun 2017 14:24:27 +0100	[thread overview]
Message-ID: <272d73ed-5bb3-88b2-13c7-ab3b061ee0c0@arm.com> (raw)
In-Reply-To: <e9c679de-01a6-440d-f009-ad419682f4fa@arm.com>

On 09/06/17 14:20, Julien Grall wrote:
> Hi Jan,
>
> On 08/06/17 16:19, Jan Beulich wrote:
>> Correct respective comments.
>>
>> Signed-off-by: Jan Beulich <jbeulich@suse.com>
>> ---
>> MMUEXT_{CLEAR,COPY}_PAGE in fact also allow to be invoked on DOMID_IO
>> owned pages at present. I've intentionally not added this to the text,
>> as I'm not sure we really mean to allow this. If we do, I think the
>> operation should also be allowed for MMIO pages not happening to have
>> an associated struct page_info.
>>
>> --- a/xen/include/public/xen.h
>> +++ b/xen/include/public/xen.h
>> @@ -550,16 +550,19 @@ DEFINE_XEN_GUEST_HANDLE(mmuext_op_t);
>>   * is useful to ensure that no mappings to the OS's own heap are
>> accidentally
>>   * installed. (e.g., in Linux this could cause havoc as reference counts
>>   * aren't adjusted on the I/O-mapping code path).
>> - * This only makes sense in MMUEXT_SET_FOREIGNDOM, but in that
>> context can
>> - * be specified by any calling domain.
>> + * This only makes sense as HYPERVISOR_mmu_update()'s and
>> + * HYPERVISOR_update_va_mapping_otherdomain()'s "foreigndom"
>> argument. For
>> + * HYPERVISOR_mmu_update() context it can be specified by any calling
>> domain,
>> + * otherwise it's only permitted if the caller is privileged.
>>   */
>>  #define DOMID_IO             xen_mk_uint(0x7FF1)
>>
>>  /*
>>   * DOMID_XEN is used to allow privileged domains to map restricted
>> parts of
>>   * Xen's heap space (e.g., the machine_to_phys table).
>> - * This only makes sense in MMUEXT_SET_FOREIGNDOM, and is only
>> permitted if
>> - * the caller is privileged.
>> + * This only makes sense as HYPERVISOR_mmu_update()'s,
>> HYPERVISOR_mmuext_op()'s,
>> + * or HYPERVISOR_update_va_mapping_otherdomain()'s "foreigndom"
>> argument, and is
>> + * only permitted if the caller is privileged.
>
> DOMID_XEN is used on ARM for mapping Xen buffer (e.g trace) using

s/is/will be/ as the series has not yet been merged (see [1]). But to 
clarify, xentrace is currently call xc_map_foreign_pages which will 
turned into a physmap hypercall for ARM and x86 HVM guests.

> physmap hypercall with XENMAPSPACE_foreign_gmfn_foreign.

Cheers,

[1] https://patchwork.kernel.org/patch/8604811/

-- 
Julien Grall

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