linux-kernel - RE: [PATCH 10/13] x86/hyper-v: Add HvFlushGuestAddressList hypercall support

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Date:   Wed, 12 Sep 2018 00:22:24 +0000
From:   "Michael Kelley (EOSG)" <Michael.H.Kelley@...rosoft.com>
To:     Tianyu Lan <Tianyu.Lan@...rosoft.com>
CC:     KY Srinivasan <kys@...rosoft.com>,
        Haiyang Zhang <haiyangz@...rosoft.com>,
        Stephen Hemminger <sthemmin@...rosoft.com>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "mingo@...hat.com" <mingo@...hat.com>,
        "hpa@...or.com" <hpa@...or.com>, "x86@...nel.org" <x86@...nel.org>,
        "pbonzini@...hat.com" <pbonzini@...hat.com>,
        "rkrcmar@...hat.com" <rkrcmar@...hat.com>,
        "devel@...uxdriverproject.org" <devel@...uxdriverproject.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        vkuznets <vkuznets@...hat.com>,
        Jork Loeser <Jork.Loeser@...rosoft.com>
Subject: RE: [PATCH 10/13] x86/hyper-v: Add HvFlushGuestAddressList hypercall
 support

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.

> +{
> +	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