linux-kernel - Re: [PATCH v2 01/43] KVM: Prepare for handling only shared mappings in mmu

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Message-ID: <ZirfnPFPo1cMwFQc@google.com>
Date: Thu, 25 Apr 2024 15:56:28 -0700
From: Sean Christopherson <seanjc@...gle.com>
To: Steven Price <steven.price@....com>
Cc: Fuad Tabba <tabba@...gle.com>, kvm@...r.kernel.org, kvmarm@...ts.linux.dev, 
	Catalin Marinas <catalin.marinas@....com>, Marc Zyngier <maz@...nel.org>, Will Deacon <will@...nel.org>, 
	James Morse <james.morse@....com>, Oliver Upton <oliver.upton@...ux.dev>, 
	Suzuki K Poulose <suzuki.poulose@....com>, Zenghui Yu <yuzenghui@...wei.com>, 
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org, 
	Joey Gouly <joey.gouly@....com>, Alexandru Elisei <alexandru.elisei@....com>, 
	Christoffer Dall <christoffer.dall@....com>, linux-coco@...ts.linux.dev, 
	Ganapatrao Kulkarni <gankulkarni@...amperecomputing.com>
Subject: Re: [PATCH v2 01/43] KVM: Prepare for handling only shared mappings
 in mmu_notifier events

On Thu, Apr 25, 2024, Steven Price wrote:
> On 25/04/2024 10:48, Fuad Tabba wrote:
> > On Fri, Apr 12, 2024 at 9:43 AM Steven Price <steven.price@....com> wrote:
> >>  bool kvm_unmap_gfn_range(struct kvm *kvm, struct kvm_gfn_range *range);
> >> diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> >> index fb49c2a60200..3486ceef6f4e 100644
> >> --- a/virt/kvm/kvm_main.c
> >> +++ b/virt/kvm/kvm_main.c
> >> @@ -633,6 +633,13 @@ static __always_inline kvm_mn_ret_t __kvm_handle_hva_range(struct kvm *kvm,
> >>                          * the second or later invocation of the handler).
> >>                          */
> >>                         gfn_range.arg = range->arg;
> >> +
> >> +                       /*
> >> +                        * HVA-based notifications aren't relevant to private
> >> +                        * mappings as they don't have a userspace mapping.
> >> +                        */
> >> +                       gfn_range.only_private = false;
> >> +                       gfn_range.only_shared = true;
> >>                         gfn_range.may_block = range->may_block;
> > 
> > I'd discussed this with Sean when he posted this earlier. Having two
> > booleans to encode three valid states could be confusing. In response,
> > Sean suggested using an enum instead:
> > https://lore.kernel.org/all/ZUO1Giju0GkUdF0o@google.com/
> 
> That would work fine too! Unless I've missed it Sean hasn't posted an
> updated patch. My assumption is that this will get merged (in whatever
> form) before the rest of the series as part of that other series. It
> shouldn't be too hard to adapt.

Yeah, there's no updated patch.

Fuad, if you have a strong preference, I recommend chiming in on the TDX series[*],
as that is the series that's likely going to be the first user, and I don't have
a strong preference on bools versus an enum.

[*] https://lore.kernel.org/all/e324ff5e47e07505648c0092a5370ac9ddd72f0b.1708933498.git.isaku.yamahata@intel.com