Re: [PATCH 10/13] x86/hyper-v: Add HvFlushGuestAddressList hypercall support

[Tianyu Lan <Tianyu.Lan@microsoft.com>]

Hi Michael:
	Thanks for your review.

On 9/12/2018 8:22 AM, Michael Kelley (EOSG) wrote:
> From: Tianyu Lan  Sent: Monday, September 10, 2018 1:39 AM
>> +
>> +int hyperv_flush_guest_mapping_range(u64 as, struct kvm_tlb_range *range)
> 
> I'm really concerned about defining the Hyper-V function to flush
> guest mappings in terms of a KVM struct definition.  Your patch puts
> this function in arch/x86/hyperv/nested.c.  I haven't investigated all
> the details, but on its face this approach seems like it would cause
> trouble in the long run, and it doesn't support the case of a
> hypervisor other than KVM running at L1.
> 
> I know that KVM code has taken a dependency on Hyper-V types and
> code, but that's because KVM is emulating a lot of Hyper-V functionality
> and it's taking advantage of Hyper-V enlightenments.  Is there a top
> level reason I haven't thought of for Hyper-V code to take a
> dependency on KVM definitions?  I would think we want Hyper-V
> code to be generic, using Hyper-V data structure definitions.  Then in
> keeping with what's already been done, KVM code would use those
> definitions where it needs to make calls to Hyper-V code.
>

I think KVM is only one kernel-based hypervisor and is only caller of 
nested hypercalls. So I reused KVM data structure in the new function.
I will make it more general in the next version.

>> +{
>> +	struct kvm_mmu_page *sp;
>> +	struct hv_guest_mapping_flush_list **flush_pcpu;
>> +	struct hv_guest_mapping_flush_list *flush;
>> +	u64 status = 0;
>> +	unsigned long flags;
>> +	int ret = -ENOTSUPP;
>> +	int gpa_n = 0;
>> +
>> +	if (!hv_hypercall_pg)
>> +		goto fault;
>> +
>> +	local_irq_save(flags);
>> +
>> +	flush_pcpu = (struct hv_guest_mapping_flush_list **)
>> +		this_cpu_ptr(hyperv_pcpu_input_arg);
>> +
>> +	flush = *flush_pcpu;
>> +	if (unlikely(!flush)) {
>> +		local_irq_restore(flags);
>> +		goto fault;
>> +	}
>> +
>> +	flush->address_space = as;
>> +	flush->flags = 0;
>> +
>> +	if (!range->flush_list) {
>> +		gpa_n = fill_flush_list(flush->gpa_list, gpa_n,
>> +				range->start_gfn, range->end_gfn);
>> +	} else {
>> +		list_for_each_entry(sp, range->flush_list,
>> +				flush_link) {
>> +			u64 end_gfn = sp->gfn +
>> +				KVM_PAGES_PER_HPAGE(sp->role.level) - 1;
>> +			gpa_n = fill_flush_list(flush->gpa_list, gpa_n,
>> +					sp->gfn, end_gfn);
>> +		}
> 
> Per the previous comment, if this loop really needs to walk a KVM
> data structure, look for a different way to organize things so that
> the handling of KVM-specific data structures is in code that’s part
> of KVM, rather than in Hyper-V code.
> 
> Michael
>