linux-kernel - [PATCH 2/2] KVM: arm64: Skip the cache flush when coalescing tables into a block

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Date:   Mon, 25 Jan 2021 22:10:44 +0800
From:   Yanan Wang <wangyanan55@...wei.com>
To:     Marc Zyngier <maz@...nel.org>, Will Deacon <will@...nel.org>,
        "Catalin Marinas" <catalin.marinas@....com>,
        James Morse <james.morse@....com>,
        "Julien Thierry" <julien.thierry.kdev@...il.com>,
        Suzuki K Poulose <suzuki.poulose@....com>,
        <kvmarm@...ts.cs.columbia.edu>,
        <linux-arm-kernel@...ts.infradead.org>, <kvm@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>
CC:     <wanghaibin.wang@...wei.com>, <yuzenghui@...wei.com>,
        Yanan Wang <wangyanan55@...wei.com>
Subject: [PATCH 2/2] KVM: arm64: Skip the cache flush when coalescing tables into a block

After dirty-logging is stopped for a VM configured with huge mappings,
KVM will recover the table mappings back to block mappings. As we only
replace the existing page tables with a block entry and the cacheability
has not been changed, the cache maintenance opreations can be skipped.

Signed-off-by: Yanan Wang <wangyanan55@...wei.com>
---
 arch/arm64/kvm/mmu.c | 12 +++++++++---
 1 file changed, 9 insertions(+), 3 deletions(-)

diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c
index 8e8549ea1d70..37b427dcbc4f 100644
--- a/arch/arm64/kvm/mmu.c
+++ b/arch/arm64/kvm/mmu.c
@@ -744,7 +744,7 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
 {
 	int ret = 0;
 	bool write_fault, writable, force_pte = false;
-	bool exec_fault;
+	bool exec_fault, adjust_hugepage;
 	bool device = false;
 	unsigned long mmu_seq;
 	struct kvm *kvm = vcpu->kvm;
@@ -872,12 +872,18 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
 		mark_page_dirty(kvm, gfn);
 	}
 
-	if (fault_status != FSC_PERM && !device)
+	/*
+	 * There is no necessity to perform cache maintenance operations if we
+	 * will only replace the existing table mappings with a block mapping.
+	 */
+	adjust_hugepage = fault_granule < vma_pagesize ? true : false;
+	if (fault_status != FSC_PERM && !device && !adjust_hugepage)
 		clean_dcache_guest_page(pfn, vma_pagesize);
 
 	if (exec_fault) {
 		prot |= KVM_PGTABLE_PROT_X;
-		invalidate_icache_guest_page(pfn, vma_pagesize);
+		if (!adjust_hugepage)
+			invalidate_icache_guest_page(pfn, vma_pagesize);
 	}
 
 	if (device)
-- 
2.19.1