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Date: Fri, 26 Apr 2024 09:49:53 -0700
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Message-ID: <ZivazWQw1oCU8VBC@google.com>
Subject: Re: [PATCH v19 011/130] KVM: Add new members to struct kvm_gfn_range
 to operate on
From: Sean Christopherson <seanjc@google.com>
To: Rick P Edgecombe <rick.p.edgecombe@intel.com>
Cc: Tina Zhang <tina.zhang@intel.com>, 
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>, Hang Yuan <hang.yuan@intel.com>, 
	Kai Huang <kai.huang@intel.com>, 
	"binbin.wu@linux.intel.com" <binbin.wu@linux.intel.com>, "sagis@google.com" <sagis@google.com>, 
	Bo Chen <chen.bo@intel.com>, 
	"isaku.yamahata@linux.intel.com" <isaku.yamahata@linux.intel.com>, "tabba@google.com" <tabba@google.com>, 
	Erdem Aktas <erdemaktas@google.com>, 
	"isaku.yamahata@gmail.com" <isaku.yamahata@gmail.com>, "kvm@vger.kernel.org" <kvm@vger.kernel.org>, 
	Isaku Yamahata <isaku.yamahata@intel.com>, "pbonzini@redhat.com" <pbonzini@redhat.com>
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On Fri, Apr 26, 2024, Rick P Edgecombe wrote:
> On Fri, 2024-04-26 at 08:28 -0700, Sean Christopherson wrote:
> > If the choice is between an enum and exclude_*, I would strongly prefer the
> > enum.  Using exclude_* results in inverted polarity for the code that
> > triggers invalidations.
> 
> Right, the awkwardness lands in that code.
> 
> The processing code looks nice though:
> https://lore.kernel.org/kvm/5210e6e6e2eb73b04cb7039084015612479ae2fe.camel@intel.com/

Heh, where's your bitmask abuse spirit?  It's a little evil (and by "evil" I mean
awesome), but the need to process different roots is another good argument for an
enum+bitmask.

enum tdp_mmu_root_types {
	KVM_SHARED_ROOTS = KVM_PROCESS_SHARED,
	KVM_PRIVATE_ROOTS = KVM_PROCESS_PRIVATE,
	KVM_VALID_ROOTS = BIT(2),
	KVM_ANY_VALID_ROOT = KVM_SHARED_ROOT | KVM_PRIVATE_ROOT | KVM_VALID_ROOT,
	KVM_ANY_ROOT = KVM_SHARED_ROOT | KVM_PRIVATE_ROOT,
}
static_assert(!(KVM_SHARED_ROOTS & KVM_VALID_ROOTS));
static_assert(!(KVM_PRIVATE_ROOTS & KVM_VALID_ROOTS));
static_assert(KVM_PRIVATE_ROOTS == (KVM_SHARED_ROOTS << 1));

/*
 * Returns the next root after @prev_root (or the first root if @prev_root is
 * NULL).  A reference to the returned root is acquired, and the reference to
 * @prev_root is released (the caller obviously must hold a reference to
 * @prev_root if it's non-NULL).
 *
 * Returns NULL if the end of tdp_mmu_roots was reached.
 */
static struct kvm_mmu_page *tdp_mmu_next_root(struct kvm *kvm,
					      struct kvm_mmu_page *prev_root,
					      enum tdp_mmu_root_types types)
{
	bool only_valid = types & KVM_VALID_ROOTS;
	struct kvm_mmu_page *next_root;

	/*
	 * While the roots themselves are RCU-protected, fields such as
	 * role.invalid are protected by mmu_lock.
	 */
	lockdep_assert_held(&kvm->mmu_lock);

	rcu_read_lock();

	if (prev_root)
		next_root = list_next_or_null_rcu(&kvm->arch.tdp_mmu_roots,
						  &prev_root->link,
						  typeof(*prev_root), link);
	else
		next_root = list_first_or_null_rcu(&kvm->arch.tdp_mmu_roots,
						   typeof(*next_root), link);

	while (next_root) {
		if ((!only_valid || !next_root->role.invalid) &&
		    (types & (KVM_SHARED_ROOTS << is_private_sp(root))) &&
		    kvm_tdp_mmu_get_root(next_root))
			break;

		next_root = list_next_or_null_rcu(&kvm->arch.tdp_mmu_roots,
				&next_root->link, typeof(*next_root), link);
	}

	rcu_read_unlock();

	if (prev_root)
		kvm_tdp_mmu_put_root(kvm, prev_root);

	return next_root;
}

#define __for_each_tdp_mmu_root_yield_safe(_kvm, _root, _as_id, _types)		\
	for (_root = tdp_mmu_next_root(_kvm, NULL, _types);			\
	     ({ lockdep_assert_held(&(_kvm)->mmu_lock); }), _root;		\
	     _root = tdp_mmu_next_root(_kvm, _root, _types))			\
		if (_as_id >= 0 && kvm_mmu_page_as_id(_root) != _as_id) {	\
		} else

#define for_each_valid_tdp_mmu_root_yield_safe(_kvm, _root, _as_id)		\
	__for_each_tdp_mmu_root_yield_safe(_kvm, _root, _as_id, KVM_ANY_VALID_ROOT)

#define for_each_tdp_mmu_root_yield_safe(_kvm, _root)				\
	for (_root = tdp_mmu_next_root(_kvm, NULL, KVM_ANY_ROOT);		\
	     ({ lockdep_assert_held(&(_kvm)->mmu_lock); }), _root;		\
	     _root = tdp_mmu_next_root(_kvm, _root, KVM_ANY_ROOT))