From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) (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 677693D810D for ; Wed, 8 Apr 2026 15:42:31 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=170.10.129.124 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1775662953; cv=none; b=jD96A7Govj/YXmCriHKkzBpipc+PSmSLQ9l6BC4sTu9Y35/A7DM9RvrFgwNvKRK4zmCTUspTDAqwqi5hH9af2Qr/pNecKAhE/2f2aJZPBrDqVZ4SYS3P+5MgdIkxYxiZfUTqdhW/g9yn0I4ieQbrp0uo2fzsot7dDsQMrX+SQhI= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1775662953; c=relaxed/simple; bh=xEYy5dAYYS2A2/VZh1lSZF372/3b8XaObXPJLU+7krk=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version:Content-Type; b=bajPAgiVbWe9D2LHOKVYl2I77MGNpQ9T7hu36DF1fRLIYz5GisbMamytPgeLrY/xHcMkQVhFMqENBhF9rzQue0MlS7ylEGpjza+YtbbKJ+Gos7X+7qxysw9j8a2624rJcnlKfBF7NallRrCMvLiSOtMzEDF0Ubp4vC5o+efVQYg= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=redhat.com; spf=pass smtp.mailfrom=redhat.com; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b=P8+ePmET; arc=none smtp.client-ip=170.10.129.124 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=redhat.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=redhat.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="P8+ePmET" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1775662950; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=T6bknSVJlYMJRJsVKlIB214gfQ9ySZOyYvJd1kpHdpY=; b=P8+ePmETh1FIPI7bf3iDx19ZA2DJz3LEhh+OyHB3xYP7neuMz7wmMHhwEGUNyDyTZmeVTG 1VRKTTzri9Oe9n3IOxnGscZ0mv1eE7Z4RJNQ0F2M3XIIKyOBbPcP3ljX4KZl68cO+VCXSF GbLm93lFBAi9ISc+soI7Mqx0BQeYsCA= Received: from mx-prod-mc-01.mail-002.prod.us-west-2.aws.redhat.com (ec2-54-186-198-63.us-west-2.compute.amazonaws.com [54.186.198.63]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-5-wCIx5at7P1iuQs8UeNZZqw-1; Wed, 08 Apr 2026 11:42:27 -0400 X-MC-Unique: wCIx5at7P1iuQs8UeNZZqw-1 X-Mimecast-MFC-AGG-ID: wCIx5at7P1iuQs8UeNZZqw_1775662946 Received: from mx-prod-int-06.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-06.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.93]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by mx-prod-mc-01.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 0633D19560B2; Wed, 8 Apr 2026 15:42:26 +0000 (UTC) Received: from virtlab1023.lab.eng.rdu2.redhat.lab.eng.rdu2.redhat.com (virtlab1023.lab.eng.rdu2.redhat.com [10.8.1.187]) by mx-prod-int-06.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTP id 25F5E1800764; Wed, 8 Apr 2026 15:42:25 +0000 (UTC) From: Paolo Bonzini To: linux-kernel@vger.kernel.org, kvm@vger.kernel.org Cc: Jon Kohler , Nikunj A Dadhania , Amit Shah , Sean Christopherson , Marcelo Tosatti Subject: [PATCH 07/27] KVM: x86/mmu: rename and clarify BYTE_MASK Date: Wed, 8 Apr 2026 11:41:57 -0400 Message-ID: <20260408154217.458420-8-pbonzini@redhat.com> In-Reply-To: <20260408154217.458420-1-pbonzini@redhat.com> References: <20260408154217.458420-1-pbonzini@redhat.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain Content-Transfer-Encoding: 8bit X-Scanned-By: MIMEDefang 3.4.1 on 10.30.177.93 The BYTE_MASK macro is the central point of the black magic in update_permission_bitmask(). Rename it to something that relates to how it is used, and add a comment explaining how it works. Using shifts instead of powers of two was actually suggested by David Hildenbrand back in 2017 for clarity[1] but I evidently forgot his suggestion when applying to kvm.git. [1] https://lore.kernel.org/kvm/e4b5df86-31ae-2f4e-0666-393753e256df@redhat.com/ Signed-off-by: Paolo Bonzini --- arch/x86/kvm/mmu/mmu.c | 55 ++++++++++++++++++++++++++++++------------ 1 file changed, 39 insertions(+), 16 deletions(-) diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c index dd06453d5b72..d4bb693b3555 100644 --- a/arch/x86/kvm/mmu/mmu.c +++ b/arch/x86/kvm/mmu/mmu.c @@ -5520,29 +5520,53 @@ reset_ept_shadow_zero_bits_mask(struct kvm_mmu *context, bool execonly) max_huge_page_level); } -#define BYTE_MASK(access) \ - ((1 & (access) ? 2 : 0) | \ - (2 & (access) ? 4 : 0) | \ - (3 & (access) ? 8 : 0) | \ - (4 & (access) ? 16 : 0) | \ - (5 & (access) ? 32 : 0) | \ - (6 & (access) ? 64 : 0) | \ - (7 & (access) ? 128 : 0)) - +/* + * Build a mask with all combinations of PTE access rights that + * include the given access bit. The mask can be queried with + * "mask & (1 << access)", where access is a combination of + * ACC_* bits. + * + * By mixing and matching multiple masks returned by ACC_BITS_MASK, + * update_permission_bitmask() builds what is effectively a + * two-dimensional array of bools. The second dimension is + * provided by individual bits of permissions[pfec >> 1], and + * logical &, | and ~ operations operate on all the 8 possible + * combinations of ACC_* bits. + */ +#define ACC_BITS_MASK(access) \ + ((1 & (access) ? 1 << 1 : 0) | \ + (2 & (access) ? 1 << 2 : 0) | \ + (3 & (access) ? 1 << 3 : 0) | \ + (4 & (access) ? 1 << 4 : 0) | \ + (5 & (access) ? 1 << 5 : 0) | \ + (6 & (access) ? 1 << 6 : 0) | \ + (7 & (access) ? 1 << 7 : 0)) static void update_permission_bitmask(struct kvm_mmu *mmu, bool ept) { unsigned byte; - const u8 x = BYTE_MASK(ACC_EXEC_MASK); - const u8 w = BYTE_MASK(ACC_WRITE_MASK); - const u8 u = BYTE_MASK(ACC_USER_MASK); + const u8 x = ACC_BITS_MASK(ACC_EXEC_MASK); + const u8 w = ACC_BITS_MASK(ACC_WRITE_MASK); + const u8 u = ACC_BITS_MASK(ACC_USER_MASK); bool cr4_smep = is_cr4_smep(mmu); bool cr4_smap = is_cr4_smap(mmu); bool cr0_wp = is_cr0_wp(mmu); bool efer_nx = is_efer_nx(mmu); + /* + * In hardware, page fault error codes are generated (as the name + * suggests) on any kind of page fault. permission_fault() and + * paging_tmpl.h already use the same bits after a successful page + * table walk, to indicate the kind of access being performed. + * + * However, PFERR_PRESENT_MASK and PFERR_RSVD_MASK are never set here, + * exactly because the page walk is successful. PFERR_PRESENT_MASK is + * removed by the shift, while PFERR_RSVD_MASK is repurposed in + * permission_fault() to indicate accesses that are *not* subject to + * SMAP restrictions. + */ for (byte = 0; byte < ARRAY_SIZE(mmu->permissions); ++byte) { unsigned pfec = byte << 1; @@ -5589,10 +5613,9 @@ static void update_permission_bitmask(struct kvm_mmu *mmu, bool ept) * - The access is supervisor mode * - If implicit supervisor access or X86_EFLAGS_AC is clear * - * Here, we cover the first four conditions. - * The fifth is computed dynamically in permission_fault(); - * PFERR_RSVD_MASK bit will be set in PFEC if the access is - * *not* subject to SMAP restrictions. + * Here, we cover the first four conditions. The fifth + * is computed dynamically in permission_fault() and + * communicated by setting PFERR_RSVD_MASK. */ if (cr4_smap) smapf = (pfec & (PFERR_RSVD_MASK|PFERR_FETCH_MASK)) ? 0 : kf; -- 2.52.0