Re: [Xen-devel] [PATCH for-4.11] x86/XPTI: Fix up stale comments concerning mappings

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 25.05.18 at 13:31, <andrew.cooper3@xxxxxxxxxx> wrote:
> On 25/05/18 12:17, Jan Beulich wrote:
>>>>> On 25.05.18 at 12:52, <andrew.cooper3@xxxxxxxxxx> wrote:
>>> --- a/xen/arch/x86/smpboot.c
>>> +++ b/xen/arch/x86/smpboot.c
>>> @@ -794,7 +794,7 @@ static int setup_cpu_root_pgt(unsigned int cpu)
>>>      /* SH_LINEAR_PT inserted together with guest mappings. */
>>>      /* PERDOMAIN inserted during context switch. */
>>>  
>>> -    /* One-time setup of common_pgt, which maps .text.entry and the stubs. 
> */
>>> +    /* One-time setup of common_pgt, which maps .text.entry. */
>>>      if ( unlikely(!root_get_intpte(common_pgt)) )
>>>      {
>>>          const char *ptr;
>> I don't understand this removal - common_pgt still is used to map the stubs.
> 
> Hang on.  If this is the case, then surely you SP3 fix need to retain
> its "no other CPUs using this mapping" check when destroying the mapping.

No. All the CPUs share the L4 and L3 entries, but L2 entries may differ
(when there are more than 512 CPUs), and L1 entries will be distinct for
all CPUs. (I take it you mean "S3 fix" rather than "SP3 fix".)

>> It is just that the addition of the leaf entry for the stub space now happens
>> later. If you really want to change it, how about "One-time setup of
>> common_pgt and its .text.entry mappings"?
>>
>>> @@ -811,7 +811,7 @@ static int setup_cpu_root_pgt(unsigned int cpu)
>>>  
>>>      rpt[root_table_offset(XEN_VIRT_START)] = common_pgt;
>>>  
>>> -    /* Install direct map page table entries for stack, IDT, and TSS. */
>>> +    /* Install per-pcpu mappings for the stack, IDT, TSS and stubs. */
>> Just for my own education: Back in school (i.e. quite long ago) I had been
>> told that in such enumerations - specifically other than in German - a
>> comma also belongs right ahead of the "and". Is that not the case anymore
>> nowadays?
> 
> This known as "The Oxford Comma".

Ouch - and I've asked someone sitting in Cambridge. ;-)

Jan



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