From 936190fcfcf66695348127992249051467de7072 Mon Sep 17 00:00:00 2001 From: Fangyu Yu Date: Wed, 10 Jun 2026 17:39:22 +0800 Subject: [PATCH] RISC-V: KVM: Avoid redundant page-table allocations in ioremap topup kvm_riscv_mmu_ioremap() currently tops up its on-stack page-table cache via kvm_mmu_topup_memory_cache(), which allocates up to KVM_ARCH_NR_OBJS_PER_MEMORY_CACHE (32) objects per topup. ioremap only consumes non-leaf page-table pages, at most pgd_levels - 1 (1 to 4) per call, and for contiguous mappings within the same huge page the non-leaf pages are allocated once and reused by subsequent pages. Topping up to 32 objects therefore triggers many unnecessary GFP_KERNEL_ACCOUNT allocations on every call, all of which are freed when the function returns. In hot paths (such as vCPU migration), this creates avoidable allocator churn and wastes CPU cycles. Use __kvm_mmu_topup_memory_cache() with a capacity of pgd_levels so the on-stack cache is sized to the maximum demand of a single mapping. This removes the redundant allocations and reduces per-call overhead without changing behavior. Reviewed-by: Anup Patel Signed-off-by: Fangyu Yu Link: https://lore.kernel.org/r/20260610093922.51617-1-fangyu.yu@linux.alibaba.com Signed-off-by: Anup Patel --- arch/riscv/kvm/mmu.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/arch/riscv/kvm/mmu.c b/arch/riscv/kvm/mmu.c index 082f9b261733..8a0aa5e0e216 100644 --- a/arch/riscv/kvm/mmu.c +++ b/arch/riscv/kvm/mmu.c @@ -41,6 +41,7 @@ int kvm_riscv_mmu_ioremap(struct kvm *kvm, gpa_t gpa, phys_addr_t hpa, pgprot_t prot; unsigned long pfn; phys_addr_t addr, end; + unsigned long pgd_levels = kvm->arch.pgd_levels; struct kvm_mmu_memory_cache pcache = { .gfp_custom = (in_atomic) ? GFP_ATOMIC | __GFP_ACCOUNT : 0, .gfp_zero = __GFP_ZERO, @@ -63,7 +64,7 @@ int kvm_riscv_mmu_ioremap(struct kvm *kvm, gpa_t gpa, phys_addr_t hpa, if (!writable) map.pte = pte_wrprotect(map.pte); - ret = kvm_mmu_topup_memory_cache(&pcache, kvm->arch.pgd_levels); + ret = __kvm_mmu_topup_memory_cache(&pcache, pgd_levels, pgd_levels); if (ret) goto out;