Re: [Xen-devel] [PATCH 2/3] VMX: allocate VMCS pages from domain heap

["Jan Beulich" <jbeulich@xxxxxxxx>]

>>> "Tian, Kevin" <kevin.tian@xxxxxxxxx> 10/21/15 5:16 AM >>>
>> From: Jan Beulich [mailto:JBeulich@xxxxxxxx]
>> Sent: Tuesday, October 20, 2015 6:36 PM
>> >>> On 20.10.15 at 12:12, <andrew.cooper3@xxxxxxxxxx> wrote:
>> > On 19/10/15 16:22, Jan Beulich wrote:
>> >> -static struct vmcs_struct *vmx_alloc_vmcs(void)
>> >> +static paddr_t vmx_alloc_vmcs(void)
>> >>  {
>> >> +    struct page_info *pg;
>> >>      struct vmcs_struct *vmcs;
>> >>
>> >> -    if ( (vmcs = alloc_xenheap_page()) == NULL )
>> >> +    if ( (pg = alloc_domheap_page(NULL, 0)) == NULL )
>> >
>> > As an observation, it would be good to pass v from the caller, and NUMA
>> > allocate against v->domain here.
>> 
>> Yes, in another patch.
>
>which 'another patch'? suppose not PATCH 3/3 since I didn't' see 
>related change there.

A yet to be written one.

>> >> @@ -580,7 +583,7 @@ int vmx_cpu_up_prepare(unsigned int cpu)
>> >>  void vmx_cpu_dead(unsigned int cpu)
>> >>  {
>> >>      vmx_free_vmcs(per_cpu(vmxon_region, cpu));
>> >> -    per_cpu(vmxon_region, cpu) = NULL;
>> >> +    per_cpu(vmxon_region, cpu) = 0;
>> >
>> > While this is currently safe (as pa 0 is not part of the available heap
>> > allocation range), might it be worth introducing a named sentential?  I
>> > can forsee a DMLite nested Xen scenario where we definitely don't need
>> > to treat the low 1MB magically.
>> 
>> I guess there are more things to adjust if we ever cared to recover
>> the few hundred kb below 1Mb. And then I don't see why nested
>> Xen would matter here: One major main reason for reserving that
>> space is that we want to put the trampoline there. Do you think
>> DMlite would allow us to get away without? But even if so, this
>> would again fall under what I've said in the first sentence.
>
>Could you at least introduce a macro first? Regardless of how much
>things to adjust, this way makes future change simple.

I can, just that this won't catch any other of the MFN-0-is-not-used cases
in the code base.

Jan


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