From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mgamail.intel.com (mgamail.intel.com [198.175.65.17]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 2E7674848A6; Mon, 28 Sep 2026 09:11:13 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=198.175.65.17 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1790586676; cv=none; b=aQaPGx1iiQLZeplKSEZ2AOKDrmxjkVr0uxsjiDJ3RCbjNSgXhvhfbaoQkTAO1VIPGOqbyyUJgELKXZBUgotXWGn1IcrsNVrh/dfby6FaASxs1XIMDWuOD2vmEERofBQMOAoC4AX7i6OEsoGFZvaSQRGflgoudxw2jMS31EnPnP8= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1790586676; c=relaxed/simple; bh=VUj14DSXmUTODfmfQEWnPX2yd1a4ycR6M2uRXIA0/d8=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=inq/MwaY4Pg7WQqn9yO82VUihVLWw1Y/WGAnk9Y9xYymqHqxlEGSDyzubskvRlcvQ3Lf+UhAB64s44s+38Kt0qPUiL5570Zi71NgyR3Dqnqv88Ut91lHcLH1I+kTK55O+yZmV52gEyxdWcDURNOopBT3so6sEYpwrmgZ1VTAsWY= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=intel.com; spf=pass smtp.mailfrom=intel.com; dkim=pass (2048-bit key) header.d=intel.com header.i=@intel.com header.b=ORWsAzEx; arc=none smtp.client-ip=198.175.65.17 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=intel.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=intel.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=intel.com header.i=@intel.com header.b="ORWsAzEx" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1790586674; x=1822122674; h=from:to:cc:subject:date:message-id:in-reply-to: references:mime-version:content-transfer-encoding; bh=VUj14DSXmUTODfmfQEWnPX2yd1a4ycR6M2uRXIA0/d8=; b=ORWsAzEx8seaCmQmY+5pw8L4Sg8pN+RJBaaa7IywcNIiiCwhqALC5wTf ezT7s4yLgEP8Qe94/FnvH0P2DY8lmcuU09hWo8JAKMY/aNR9SJJaI/SFb iT6xP4xnZejBf6c/8x6H2sQRUC3TSYGGENLuIIBMHn9/W7fb0L6B4RyD2 U6RxQbY4G3N8k0pVCAvgx7VxgRMSBgnq/PRcrbuQqId8wILiK/N1OYsDc 6RQZyZJPIw1C0k7Zg5bUaxT5cIC6drxZvwivkXf474VgQSNM8MO31XkYW PyY2+YH7Jh29uTaIWX8svByxi6iJgOdCt34WKu1mnFsO8lj1KJ7S88BUC w==; X-CSE-ConnectionGUID: pZKCGao8Tv6NqALNBmLbtw== X-CSE-MsgGUID: Bm8Zhs0xTgyKIR/oPIp4vA== X-IronPort-AV: E=McAfee;i="6800,10657,11918"; a="90323370" X-IronPort-AV: E=Sophos;i="6.27,128,1787036400"; d="scan'208";a="90323370" Received: from orviesa005.jf.intel.com ([10.64.159.145]) by orvoesa109.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 28 Sep 2026 02:11:14 -0700 X-CSE-ConnectionGUID: ouH18APYROOpqfuclOXg8w== X-CSE-MsgGUID: JVi7EctTT065HX6ESSeVqA== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="6.27,128,1787036400"; d="scan'208";a="278819225" Received: from yzhao56-desk.sh.intel.com ([10.239.47.61]) by orviesa005-auth.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 28 Sep 2026 02:11:08 -0700 From: Yan Zhao To: seanjc@google.com, pbonzini@redhat.com, dave.hansen@intel.com Cc: linux-kernel@vger.kernel.org, kvm@vger.kernel.org, x86@kernel.org, rick.p.edgecombe@intel.com, kas@kernel.org, tabba@google.com, ackerleytng@google.com, michael.roth@amd.com, david@kernel.org, vannapurve@google.com, sagis@google.com, vbabka@suse.cz, thomas.lendacky@amd.com, nik.borisov@suse.com, pgonda@google.com, fan.du@intel.com, jun.miao@intel.com, francescolavra.fl@gmail.com, jgross@suse.com, xiaoyao.li@intel.com, kai.huang@intel.com, binbin.wu@linux.intel.com, chao.p.peng@intel.com, chao.gao@intel.com, farrah.chen@intel.com, yan.y.zhao@intel.com Subject: [PATCH v4 08/17] KVM: TDX: Adjust the topup count of DPAMT page pairs for splitting S-EPT Date: Mon, 28 Sep 2026 17:10:35 +0800 Message-ID: <20260928091035.15599-1-yan.y.zhao@intel.com> X-Mailer: git-send-email 2.43.2 In-Reply-To: <20260928090729.15468-1-yan.y.zhao@intel.com> References: <20260928090729.15468-1-yan.y.zhao@intel.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit KVM needs to allocate enough DPAMT page pairs in the pamt_cache for consumption by both page table pages and guest pages. Since the DPAMT page pair for the S-EPT root page is already allocated during TD initialization, there is no need to allocate the DPAMT page pair for the S-EPT root page. Therefore, previously the DPAMT page pairs required equals "min_nr_spts - 1 + 1". When splitting S-EPT, min_nr_spts does not include the root SPT. So, limit the -1 calculation to when min_nr_spts equals root_level, though this will cause one pair over-allocation in the normal page fault path because PT64_ROOT_MAX_LEVEL is always passed even when launching a 4-level TD. Additionally, KVM may need to retry tdh_mem_page_demote() a second time, causing the DPAMT page pair for the guest private pages to be drawn from the pamt_cache twice in the worst case. Therefore, add an extra +1 to cover this worst-case scenario. The slight over-allocation is acceptable since KVM already pre-allocates more pages than needed (e.g., when mapping huge pages) in case of the worst-case scenario. Signed-off-by: Yan Zhao --- arch/x86/kvm/vmx/tdx.c | 26 ++++++++++++++++++++++---- 1 file changed, 22 insertions(+), 4 deletions(-) diff --git a/arch/x86/kvm/vmx/tdx.c b/arch/x86/kvm/vmx/tdx.c index 3186c4808cae..397a308b834c 100644 --- a/arch/x86/kvm/vmx/tdx.c +++ b/arch/x86/kvm/vmx/tdx.c @@ -1630,16 +1630,34 @@ void tdx_load_mmu_pgd(struct kvm_vcpu *vcpu, hpa_t root_hpa, int pgd_level) static int tdx_topup_external_pamt_cache(struct kvm_vcpu *vcpu, int min_nr_spts) { + int dpamt_pairs; + if (WARN_ON_ONCE(!vcpu)) return -EIO; + /* Exclude the root SPT, as its DPAMT page pair is already installed */ + if (min_nr_spts == vcpu->kvm->arch.mirror_root_level) + min_nr_spts -= 1; + + /* + * Each S-EPT page table page + 4KB guest private page needs a pair of + * DPAMT pages. + */ + dpamt_pairs = min_nr_spts + 1; + /* - * Minus one page to exclude the root SPT, but plus one page for a - * possible 4KB private mapping. + * After each topup, KVM may invoke DEMOTE at most twice. The first + * DEMOTE invocation draws two pairs of pages from the cache: one for + * the S-EPT page table page and one for the guest private memory. + * Since these pages are not returned to the cache, the second DEMOTE + * invocation still needs to consume one additional pair for the guest + * private memory (the pair for the S-EPT page table page is reused for + * the 2nd invocation). Increase the topup count to account for this + * worst-case scenario. */ - min_nr_spts += -1 + 1; + dpamt_pairs += 1; - return tdx_topup_pamt_cache(&to_tdx(vcpu)->pamt_cache, min_nr_spts); + return tdx_topup_pamt_cache(&to_tdx(vcpu)->pamt_cache, dpamt_pairs); } static int tdx_mem_page_add(struct kvm *kvm, gfn_t gfn, enum pg_level level, -- 2.43.2