Re: [Xen-devel] [PATCH v2 4/4] x86: support "pv-l1tf=default"

2018-10-04 Thread Jan Beulich 
>>> On 02.10.18 at 18:59,  wrote:
> On 01/10/18 13:11, Jan Beulich wrote:
>> Just like the otherwise similar "xpti=" allows for, to revert back to
>> built-in defaults.
>>
>> Signed-off-by: Jan Beulich 
> 
> I've made my opinion on this matter clear on several occasions.
> 
> This is not a change I'm happy with taking.

I knew you would say this, but I still don't understand why you think
you need to block something that _doesn't harm_ anyone when not
used, but is useful to certain people. As previously said, I in particular
don't buy your argument of this adding further complexity to the
interactions of command line options, most specifically the dependency
of overall effect on their ordering on the command line: This is
something which has always been there, and doesn't get made any
worse at all with this addition.

In the end you could submit a patch to remove the "default" sub-
option from xpti (with whatever rationale), and I could similarly
refuse to ack it. We'd then be stuck forever with two similar but
inconsistent command line options. Not a very nice situation...

Jan



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Re: [Xen-devel] [PATCH v2 4/4] x86: support "pv-l1tf=default"

2018-10-02 Thread Andrew Cooper 
On 01/10/18 13:11, Jan Beulich wrote:
> Just like the otherwise similar "xpti=" allows for, to revert back to
> built-in defaults.
>
> Signed-off-by: Jan Beulich 

I've made my opinion on this matter clear on several occasions.

This is not a change I'm happy with taking.

~Andrew

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[Xen-devel] [PATCH v2 4/4] x86: support "pv-l1tf=default"

2018-10-01 Thread Jan Beulich 
Just like the otherwise similar "xpti=" allows for, to revert back to
built-in defaults.

Signed-off-by: Jan Beulich 
---
v2: Split out into separate patch.

--- a/docs/misc/xen-command-line.markdown
+++ b/docs/misc/xen-command-line.markdown
@@ -1604,7 +1604,7 @@ certain you don't plan on having PV gues
 turning it off can reduce the attack surface.
 
 ### pv-l1tf (x86)
-> `= List of [ , dom0=, domu= ]`
+> `= List of [ default, , dom0=, domu= ]`
 
 > Default: `false` on believed-unaffected hardware, or in pv-shim mode.
 >  `domu`  on believed-affected hardware.
--- a/xen/arch/x86/spec_ctrl.c
+++ b/xen/arch/x86/spec_ctrl.c
@@ -252,7 +252,9 @@ static __init int parse_pv_l1tf(const ch
 break;
 
 default:
-if ( (val = parse_boolean("dom0", s, ss)) >= 0 )
+if ( !strcmp(s, "default") )
+opt_pv_l1tf_hwdom = opt_pv_l1tf_domu = -1;
+else if ( (val = parse_boolean("dom0", s, ss)) >= 0 )
 opt_pv_l1tf_hwdom = val;
 else if ( (val = parse_boolean("domu", s, ss)) >= 0 )
 opt_pv_l1tf_domu = val;





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