Re: [Xen-devel] [PATCH v2 03/10] xen: extend XEN_DOMCTL_memory_mapping to handle memory policy

From: "Jan Beulich" <JBeulich@suse.com>
To: "Andrew Cooper" <andrew.cooper3@citrix.com>,
	"Stefano Stabellini" <sstabellini@kernel.org>
Cc: xen-devel <xen-devel@lists.xenproject.org>,
	Julien Grall <julien.grall@arm.com>,
	Stefano Stabellini <stefanos@xilinx.com>
Subject: Re: [Xen-devel] [PATCH v2 03/10] xen: extend XEN_DOMCTL_memory_mapping to handle memory policy
Date: Wed, 19 Jun 2019 00:53:13 -0600	[thread overview]
Message-ID: <5D09DBD9020000780023981A@prv1-mh.provo.novell.com> (raw)
In-Reply-To: <alpine.DEB.2.21.1906181612230.2072@sstabellini-ThinkPad-T480s>

>>> On 19.06.19 at 01:15, <sstabellini@kernel.org> wrote:
> On Tue, 18 Jun 2019, Stefano Stabellini wrote:
>> On Tue, 18 Jun 2019, Jan Beulich wrote:
>> > >>> On 17.06.19 at 23:28, <sstabellini@kernel.org> wrote:
>> > > On Thu, 2 May 2019, Jan Beulich wrote:
>> > >> >>> On 30.04.19 at 23:02, <sstabellini@kernel.org> wrote:
>> > >> > --- a/xen/include/public/domctl.h
>> > >> > +++ b/xen/include/public/domctl.h
>> > >> > @@ -571,12 +571,24 @@ struct xen_domctl_bind_pt_irq {
>> > >> >  */
>> > >> >  #define DPCI_ADD_MAPPING         1
>> > >> >  #define DPCI_REMOVE_MAPPING      0
>> > >> > +/*
>> > >> > + * Default memory policy. Corresponds to:
>> > >> > + * Arm: MEMORY_POLICY_ARM_DEV_nGRE
>> > >> > + * x86: MEMORY_POLICY_X86_UC
>> > >> > + */
>> > >> > +#define MEMORY_POLICY_DEFAULT    0
>> > >> > +/* x86 only. Memory type UNCACHABLE */
>> > >> > +#define MEMORY_POLICY_X86_UC     0
>> > >> 
>> > >> I'm afraid this may end up misleading, as on NPT and in
>> > >> shadow mode we use UC- instead of UC afaics. Andrew,
>> > >> do you have an opinion either way what exactly should
>> > >> be stated here?
>> > > 
>> > > Ping?
>> > 
>> > To me? I've stated my opinion.
>> 
>> I cannot name the macro "MEMORY_POLICY_X86_UC-" because it cannot end
>> with a "-". Instead, I can name it MEMORY_POLICY_X86_UC_MINUS that seems
>> to be what Linux does. I'll rename the optional xl parameter too from
>> "x86_uc" to "x86_uc_minus".
> 
> I chatted with Andrew on IRC and he suggested to get rid of the option
> entirely -- there is just one on x86 and doesn't necessarily need to be
> explicitly visible. We could only have MEMORY_POLICY_DEFAULT, and also
> remove the x86_uc setting from libxl/xl.
> 
> I am OK with this. However, given that I have already made all the
> changes to have MEMORY_POLICY_X86_UC_MINUS and x86_uc_minus everywhere,
> I'll send an update of the series with them.

Aren't we back to the question them whether to make this an Arm-
only interface? I'm having trouble seeing the value of an interface
which allows one to only "switch" from default to default.

Jan

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