Re: [PATCH v5 3/4] KVM: arm64/mmu: use gfn_to_pfn_page

From: Sean Christopherson <seanjc@google.com>
To: David Stevens <stevensd@chromium.org>
Cc: Marc Zyngier <maz@kernel.org>,
	Paolo Bonzini <pbonzini@redhat.com>,
	James Morse <james.morse@arm.com>,
	Alexandru Elisei <alexandru.elisei@arm.com>,
	Suzuki K Poulose <suzuki.poulose@arm.com>,
	Will Deacon <will@kernel.org>, Wanpeng Li <wanpengli@tencent.com>,
	Jim Mattson <jmattson@google.com>, Joerg Roedel <joro@8bytes.org>,
	linux-arm-kernel@lists.infradead.org,
	kvmarm@lists.cs.columbia.edu, linux-kernel@vger.kernel.org,
	kvm@vger.kernel.org
Subject: Re: [PATCH v5 3/4] KVM: arm64/mmu: use gfn_to_pfn_page
Date: Thu, 30 Dec 2021 19:45:56 +0000	[thread overview]
Message-ID: <Yc4MdFREYW98mzMs@google.com> (raw)
In-Reply-To: <20211129034317.2964790-4-stevensd@google.com>

On Mon, Nov 29, 2021, David Stevens wrote:
> @@ -1142,14 +1146,17 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
>  
>  	/* Mark the page dirty only if the fault is handled successfully */
>  	if (writable && !ret) {
> -		kvm_set_pfn_dirty(pfn);
> +		if (page)
> +			kvm_set_pfn_dirty(pfn);

If kvm_set_page_dirty() is changed to be less dumb:

		if (page)
			kvm_set_page_dirty(page);

>  		mark_page_dirty_in_slot(kvm, memslot, gfn);
>  	}
>  
>  out_unlock:
>  	spin_unlock(&kvm->mmu_lock);
> -	kvm_set_pfn_accessed(pfn);
> -	kvm_release_pfn_clean(pfn);
> +	if (page) {
> +		kvm_set_pfn_accessed(pfn);
> +		put_page(page);

Oof, KVM's helpers are stupid.  Take a page, convert it to a pfn, then convert it
back to a page, just to mark it dirty or put a ref.  Can you fold the below 
(completely untested) patch in before the x86/arm64 patches?  That way this code
can be:

	if (page)
		kvm_release_page_accessed(page);

and x86 can do:

	if (fault->page)
		kvm_release_page_clean(page);

instead of open-coding put_page().


From a8af0c60d7f6e77bbc7310d898211c43ae075cf8 Mon Sep 17 00:00:00 2001
From: Sean Christopherson <seanjc@google.com>
Date: Thu, 30 Dec 2021 11:40:58 -0800
Subject: [PATCH] KVM: Clean up and enhance helpers for releasing pages/pfns

Tweak kvm_release_page_clean() and kvm_release_page_dirty() to avoid
pointlessly converting to a pfn and back to a page, and add an "accessed"
variant that will be used in a future arm64 patch.

No functional change intended.

Signed-off-by: Sean Christopherson <seanjc@google.com>
---
 virt/kvm/kvm_main.c | 20 ++++++++++++++------
 1 file changed, 14 insertions(+), 6 deletions(-)

diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 8eb0f762a82c..f75129f641e9 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -2876,29 +2876,37 @@ void kvm_release_page_clean(struct page *page)
 {
 	WARN_ON(is_error_page(page));

-	kvm_release_pfn_clean(page_to_pfn(page));
+	put_page(page);
 }
 EXPORT_SYMBOL_GPL(kvm_release_page_clean);

 void kvm_release_pfn_clean(kvm_pfn_t pfn)
 {
 	if (!is_error_noslot_pfn(pfn) && !kvm_is_reserved_pfn(pfn))
-		put_page(pfn_to_page(pfn));
+		kvm_release_page_clean(page);
 }
 EXPORT_SYMBOL_GPL(kvm_release_pfn_clean);

+void kvm_release_page_accessed(struct page *page)
+{
+	mark_page_accessed(page);
+
+	kvm_release_page_clean(page);
+}
+EXPORT_SYMBOL_GPL(kvm_release_page_accessed);
+
 void kvm_release_page_dirty(struct page *page)
 {
-	WARN_ON(is_error_page(page));
+	SetPageDirty(page);

-	kvm_release_pfn_dirty(page_to_pfn(page));
+	kvm_release_page_clean(page);
 }
 EXPORT_SYMBOL_GPL(kvm_release_page_dirty);

 void kvm_release_pfn_dirty(kvm_pfn_t pfn)
 {
-	kvm_set_pfn_dirty(pfn);
-	kvm_release_pfn_clean(pfn);
+	if (!kvm_is_reserved_pfn(pfn) && !kvm_is_zone_device_pfn(pfn))
+		kvm_release_page_dirty(pfn_to_page(pfn));
 }
 EXPORT_SYMBOL_GPL(kvm_release_pfn_dirty);

--
2.34.1.448.ga2b2bfdf31-goog

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