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


  • To: Jan Beulich <JBeulich@xxxxxxxx>
  • From: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
  • Date: Fri, 25 May 2018 12:31:34 +0100
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  • Cc: Juergen Gross <jgross@xxxxxxxx>, Xen-devel <xen-devel@xxxxxxxxxxxxx>
  • Delivery-date: Fri, 25 May 2018 11:31:48 +0000
  • List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
  • Openpgp: preference=signencrypt

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.

> 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".  It is one of the more argued-over
areas of English grammar, but is optional (insofar that, some places
demand its presence, some places refuse to allow it, and most don't care
either way).

~Andrew

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