From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 4515CC4332F for ; Thu, 17 Feb 2022 21:04:11 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S244651AbiBQVEX (ORCPT ); Thu, 17 Feb 2022 16:04:23 -0500 Received: from mxb-00190b01.gslb.pphosted.com ([23.128.96.19]:37832 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S243907AbiBQVEF (ORCPT ); Thu, 17 Feb 2022 16:04:05 -0500 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) by lindbergh.monkeyblade.net (Postfix) with ESMTP id 2E1F8163D79 for ; Thu, 17 Feb 2022 13:03:49 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1645131828; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=PQkaRkpDm0Ym0G1tYvl1LrDOa9a/hWfn0PzBdx+ovns=; b=etHbskm5Lbl4V9ONRGzzI/TKz+fA7f/SKnSnVvxmpiyOi0tFSAJTC0IfPJC5v9MX3DiL9F TUWMXByImwdmESm19+VvzKbncMwb70wbK1mU7PQ7Ro7NaK8p8IHoxb9Kzc8MVzBA81pF/g wlAk7YlvRMLjrGiYaqgWelOw+h3aQrg= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-588-3OA7P5LIP7OT8lIVmsVEvg-1; Thu, 17 Feb 2022 16:03:46 -0500 X-MC-Unique: 3OA7P5LIP7OT8lIVmsVEvg-1 Received: from smtp.corp.redhat.com (int-mx02.intmail.prod.int.phx2.redhat.com [10.5.11.12]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 8C2081091DA0; Thu, 17 Feb 2022 21:03:45 +0000 (UTC) Received: from virtlab701.virt.lab.eng.bos.redhat.com (virtlab701.virt.lab.eng.bos.redhat.com [10.19.152.228]) by smtp.corp.redhat.com (Postfix) with ESMTP id 3E26A46983; Thu, 17 Feb 2022 21:03:45 +0000 (UTC) From: Paolo Bonzini To: linux-kernel@vger.kernel.org, kvm@vger.kernel.org Cc: seanjc@google.com Subject: [PATCH v2 09/18] KVM: x86/mmu: look for a cached PGD when going from 32-bit to 64-bit Date: Thu, 17 Feb 2022 16:03:31 -0500 Message-Id: <20220217210340.312449-10-pbonzini@redhat.com> In-Reply-To: <20220217210340.312449-1-pbonzini@redhat.com> References: <20220217210340.312449-1-pbonzini@redhat.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Scanned-By: MIMEDefang 2.79 on 10.5.11.12 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Right now, PGD caching avoids placing a PAE root in the cache by using the old value of mmu->root_level and mmu->shadow_root_level; it does not look for a cached PGD if the old root is a PAE one, and then frees it using kvm_mmu_free_roots. Change the logic instead to free the uncacheable root early. This way, __kvm_new_mmu_pgd is able to look up the cache when going from 32-bit to 64-bit (if there is a hit, the invalid root becomes the least recently used). An example of this is nested virtualization with shadow paging, when a 64-bit L1 runs a 32-bit L2. As a side effect (which is actually the reason why this patch was written), PGD caching does not use the old value of mmu->root_level and mmu->shadow_root_level anymore. Signed-off-by: Paolo Bonzini --- arch/x86/kvm/mmu/mmu.c | 82 ++++++++++++++++++++++++++++++------------ 1 file changed, 59 insertions(+), 23 deletions(-) diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c index 0f2de811e871..da324a317000 100644 --- a/arch/x86/kvm/mmu/mmu.c +++ b/arch/x86/kvm/mmu/mmu.c @@ -4107,52 +4107,88 @@ static inline bool is_root_usable(struct kvm_mmu_root_info *root, gpa_t pgd, union kvm_mmu_page_role role) { return (role.direct || pgd == root->pgd) && - VALID_PAGE(root->hpa) && to_shadow_page(root->hpa) && + VALID_PAGE(root->hpa) && role.word == to_shadow_page(root->hpa)->role.word; } /* - * Find out if a previously cached root matching the new pgd/role is available. - * The current root is also inserted into the cache. - * If a matching root was found, it is assigned to kvm_mmu->root.hpa and true is - * returned. - * Otherwise, the LRU root from the cache is assigned to kvm_mmu->root.hpa and - * false is returned. This root should now be freed by the caller. + * Find out if a previously cached root matching the new pgd/role is available, + * and insert the current root as the MRU in the cache. + * If a matching root is found, it is assigned to kvm_mmu->root and + * true is returned. + * If no match is found, kvm_mmu->root is left invalid, the LRU root is + * evicted to make room for the current root, and false is returned. */ -static bool cached_root_available(struct kvm_vcpu *vcpu, gpa_t new_pgd, - union kvm_mmu_page_role new_role) +static bool cached_root_find_and_keep_current(struct kvm *kvm, struct kvm_mmu *mmu, + gpa_t new_pgd, + union kvm_mmu_page_role new_role) { uint i; - struct kvm_mmu *mmu = vcpu->arch.mmu; if (is_root_usable(&mmu->root, new_pgd, new_role)) return true; for (i = 0; i < KVM_MMU_NUM_PREV_ROOTS; i++) { + /* + * The swaps end up rotating the cache like this: + * C 0 1 2 3 (on entry to the function) + * 0 C 1 2 3 + * 1 C 0 2 3 + * 2 C 0 1 3 + * 3 C 0 1 2 (on exit from the loop) + */ swap(mmu->root, mmu->prev_roots[i]); - if (is_root_usable(&mmu->root, new_pgd, new_role)) - break; + return true; } - return i < KVM_MMU_NUM_PREV_ROOTS; + kvm_mmu_free_roots(kvm, mmu, KVM_MMU_ROOT_CURRENT); + return false; } -static bool fast_pgd_switch(struct kvm_vcpu *vcpu, gpa_t new_pgd, - union kvm_mmu_page_role new_role) +/* + * Find out if a previously cached root matching the new pgd/role is available. + * On entry, mmu->root is invalid. + * If a matching root is found, it is assigned to kvm_mmu->root, the LRU entry + * of the cache becomes invalid, and true is returned. + * If no match is found, kvm_mmu->root is left invalid and false is returned. + */ +static bool cached_root_find_without_current(struct kvm *kvm, struct kvm_mmu *mmu, + gpa_t new_pgd, + union kvm_mmu_page_role new_role) { - struct kvm_mmu *mmu = vcpu->arch.mmu; + uint i; + + for (i = 0; i < KVM_MMU_NUM_PREV_ROOTS; i++) + if (is_root_usable(&mmu->prev_roots[i], new_pgd, new_role)) + goto hit; + return false; + +hit: + swap(mmu->root, mmu->prev_roots[i]); + /* Bubble up the remaining roots. */ + for (; i < KVM_MMU_NUM_PREV_ROOTS - 1; i++) + mmu->prev_roots[i] = mmu->prev_roots[i + 1]; + mmu->prev_roots[i].hpa = INVALID_PAGE; + return true; +} + +static bool fast_pgd_switch(struct kvm *kvm, struct kvm_mmu *mmu, + gpa_t new_pgd, union kvm_mmu_page_role new_role) +{ /* - * For now, limit the fast switch to 64-bit hosts+VMs in order to avoid + * For now, limit the caching to 64-bit hosts+VMs in order to avoid * having to deal with PDPTEs. We may add support for 32-bit hosts/VMs * later if necessary. */ - if (mmu->shadow_root_level >= PT64_ROOT_4LEVEL && - mmu->root_level >= PT64_ROOT_4LEVEL) - return cached_root_available(vcpu, new_pgd, new_role); + if (VALID_PAGE(mmu->root.hpa) && !to_shadow_page(mmu->root.hpa)) + kvm_mmu_free_roots(kvm, mmu, KVM_MMU_ROOT_CURRENT); - return false; + if (VALID_PAGE(mmu->root.hpa)) + return cached_root_find_and_keep_current(kvm, mmu, new_pgd, new_role); + else + return cached_root_find_without_current(kvm, mmu, new_pgd, new_role); } static void __kvm_mmu_new_pgd(struct kvm_vcpu *vcpu, gpa_t new_pgd, @@ -4160,8 +4196,8 @@ static void __kvm_mmu_new_pgd(struct kvm_vcpu *vcpu, gpa_t new_pgd, { struct kvm_mmu *mmu = vcpu->arch.mmu; - if (!fast_pgd_switch(vcpu, new_pgd, new_role)) { - kvm_mmu_free_roots(vcpu->kvm, mmu, KVM_MMU_ROOT_CURRENT); + if (!fast_pgd_switch(vcpu->kvm, mmu, new_pgd, new_role)) { + /* kvm_mmu_ensure_valid_pgd will set up a new root. */ return; } -- 2.31.1