From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.remote-ip=195.135.223.130 ARC-Seal: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; cv=none; t=1793285087; b=pE1I16N0CZIlUY0vzdmZPcX0JyVuZFRGybyE5dx5+3ouD9zj3wQ1npcTm7z3C70ftjQM rZL1S2F3K/oPsykFurApBv/aZ12SC4fOSNcVl6L5WbAzo3c796fPuKKwe2vuUxZk6ReU1 zwaEDQQFVW++5RXXjpsE5LmS9Wzhqf+Sx0YwWHLrDPgPCM/0S0u38sX4pBoMOQEjdpnw9 jqFvusSZPrAb/VK+e4WAA09ee3w7ojzKK2tN12NPBga9tpNkF2MZagLFRNdhryIB9NaGV 8oMAvHV/TxYUz9m5k7ggDhID7aIYvXE5kSJwjZpD8KlkDs4yRxwU5ZHiLM1aampctBw== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1793285087; h=DMARC-Filter:Received:DKIM-Signature:DKIM-Signature:DKIM-Signature: DKIM-Signature:Received:Received:From:To:Cc:Subject:Date:Message-ID: X-Mailer:In-Reply-To:References:MIME-Version:Content-Type: Content-Transfer-Encoding:X-Spam-Flag:X-Spam-Level:X-Spamd-Result: X-Spam-Score; bh=On/WzBslNRdooO2nM6+KcAg+UNarkQsFuaUhWqaMpyc=; b=lpnZnKIaMFh6J8zzB81Hd1xm23Xiz9gW90vL+ZkaslNZJiQJKtB6QILXwyUb3kE3DUBc 8q5mGx0KYIZJLE/NUeRobJkVCt9xju7aQM0qMHYRgnO0gVTsHFcJMupJJb0uy4FRRKg2M TvtGPcm4x6Y1fa3CZVlTyd8/gMB2Ux3PS/NBFkFERc5MqqKZjVxWbjXB2UXe6WIdkIKgl ti44630LjVrDlGvQhnPDNV44FlteBYf0KE30IdsBMOvNxBoQs1sMVuk3WZm9QE8CgQyAa 8gMuyJ8LxfwPw15LKiV4dqGX9i/jAOXjUkkgPoTDY2FC2SKxu6zDyUZyKYdYF4a4Tqg== ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass header.from=suse.de; spf=pass smtp.mailfrom=suse.de; dkim=pass header.d=suse.de header.i=@suse.de header.a=rsa-sha256 header.s=susede2_rsa header.b=UrdyCeEM; dkim=pass header.d=suse.de header.i=@suse.de header.a=ed25519-sha256 header.s=susede2_ed25519 header.b=GWyd71jI; dkim=pass header.d=suse.de header.i=@suse.de header.a=rsa-sha256 header.s=susede2_rsa header.b=UrdyCeEM; dkim=neutral header.d=suse.de header.i=@suse.de header.a=ed25519-sha256 header.s=susede2_ed25519 header.b=GWyd71jI; arc=none smtp.remote-ip=195.135.223.130 Received: from smtp-out1.suse.de (smtp-out1.suse.de [195.135.223.130]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (prime256v1) server-digest SHA256) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 4BF2D606A33C; Thu, 29 Oct 2026 14:44:47 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.2 smtp.subspace.kernel.org 4BF2D606A33C Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=suse.de Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=suse.de Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key, unprotected) header.d=suse.de header.i=@suse.de header.a=rsa-sha256 header.s=susede2_rsa header.b=UrdyCeEM; dkim=pass header.d=suse.de header.i=@suse.de header.a=ed25519-sha256 header.s=susede2_ed25519 header.b=GWyd71jI; dkim=pass (1024-bit key) header.d=suse.de header.i=@suse.de header.a=rsa-sha256 header.s=susede2_rsa header.b=UrdyCeEM; dkim=neutral header.d=suse.de header.i=@suse.de header.a=ed25519-sha256 header.s=susede2_ed25519 header.b=GWyd71jI Received: from imap1.dmz-prg2.suse.org (unknown [10.150.64.97]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (4096 bits) server-digest SHA256) (No client certificate requested) by smtp-out1.suse.de (Postfix) with ESMTPS id B54C22210D; Thu, 29 Oct 2026 14:44:45 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.de; s=susede2_rsa; t=1793285085; h=from:from:reply-to: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=On/WzBslNRdooO2nM6+KcAg+UNarkQsFuaUhWqaMpyc=; b=UrdyCeEMKHhopqmzqB8HSWFgIEcKTFU4pSYcOCLxn3f/ee6De+XpoEYELmPbxsMduW0d3a 596LYkT6TmeSIL8H/20MEj37EoRurGIvmzIGn+C7tiHkb9FRgi3NS1/YJIcCio8Xnl0i2D pRhue5Oo8xf5WTkSNWH5zZ+V+BQ3HvA= DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=suse.de; s=susede2_ed25519; t=1793285085; h=from:from:reply-to: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=On/WzBslNRdooO2nM6+KcAg+UNarkQsFuaUhWqaMpyc=; b=GWyd71jI75LiMrHVSGXVpQz70/7L7+unh/faDaAFEJ33aAcmosuQKzFL6yk0+RBTU3mlPx hi/UyO4w4CAHTyCQ== Authentication-Results: smtp-out1.suse.de; none DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.de; s=susede2_rsa; t=1793285085; h=from:from:reply-to: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=On/WzBslNRdooO2nM6+KcAg+UNarkQsFuaUhWqaMpyc=; b=UrdyCeEMKHhopqmzqB8HSWFgIEcKTFU4pSYcOCLxn3f/ee6De+XpoEYELmPbxsMduW0d3a 596LYkT6TmeSIL8H/20MEj37EoRurGIvmzIGn+C7tiHkb9FRgi3NS1/YJIcCio8Xnl0i2D pRhue5Oo8xf5WTkSNWH5zZ+V+BQ3HvA= DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=suse.de; s=susede2_ed25519; t=1793285085; h=from:from:reply-to: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=On/WzBslNRdooO2nM6+KcAg+UNarkQsFuaUhWqaMpyc=; b=GWyd71jI75LiMrHVSGXVpQz70/7L7+unh/faDaAFEJ33aAcmosuQKzFL6yk0+RBTU3mlPx hi/UyO4w4CAHTyCQ== Received: from imap1.dmz-prg2.suse.org (localhost [127.0.0.1]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (4096 bits) server-digest SHA256) (No client certificate requested) by imap1.dmz-prg2.suse.org (Postfix) with ESMTPS id C9C7C1339F; Thu, 29 Oct 2026 14:44:44 +0000 (UTC) Received: from dovecot-director2.suse.de ([2a07:de40:b281:106:10:150:64:167]) by imap1.dmz-prg2.suse.org with ESMTPSA id iNqFENhb42qRUwAAD6G6ig:T5 (envelope-from ); Thu, 29 Oct 2026 14:44:44 +0000 From: =?UTF-8?q?Carlos=20L=C3=B3pez?= To: kvm@vger.kernel.org, linux-mm@kvack.org, seanjc@google.com, pbonzini@redhat.com Cc: linux-s390@vger.kernel.org, imbrenda@linux.ibm.com, =?UTF-8?q?Carlos=20L=C3=B3pez?= , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , x86@kernel.org (maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)), "H. Peter Anvin" , linux-kernel@vger.kernel.org (open list:X86 ARCHITECTURE (32-BIT AND 64-BIT)) Subject: [RFC PATCH 4/4] KVM: x86/mmu: don't zap the secondary MMU on permission upgrade Date: Thu, 29 Oct 2026 15:33:37 +0100 Message-ID: <20261029143336.390231-7-clopez@suse.de> X-Mailer: git-send-email 2.51.0 In-Reply-To: <20261029143336.390231-3-clopez@suse.de> References: <20261029143336.390231-3-clopez@suse.de> X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-Spam-Flag: NO X-Spam-Level: X-Spamd-Result: default: False [-16.30 / 50.00]; SUSE_INTERNAL_BYPASS(-9.00)[]; REPLY(-4.00)[]; BAYES_HAM(-3.00)[100.00%]; MID_CONTAINS_FROM(1.00)[]; NEURAL_HAM_LONG(-1.00)[-1.000]; NEURAL_HAM_SHORT(-0.20)[-1.000]; MIME_GOOD(-0.10)[text/plain]; RCVD_VIA_SMTP_AUTH(0.00)[]; ARC_NA(0.00)[]; MIME_TRACE(0.00)[0:+]; RCPT_COUNT_SEVEN(0.00)[11]; RCVD_TLS_ALL(0.00)[]; DKIM_SIGNED(0.00)[suse.de:s=susede2_rsa,suse.de:s=susede2_ed25519]; FROM_HAS_DN(0.00)[]; TO_DN_SOME(0.00)[]; FROM_EQ_ENVFROM(0.00)[]; RCVD_COUNT_TWO(0.00)[2]; TO_MATCH_ENVRCPT_ALL(0.00)[]; DBL_BLOCKED_OPENRESOLVER(0.00)[imap1.dmz-prg2.suse.org:helo,suse.de:email] X-Spam-Score: -16.30 When an mmu_notifier invalidation only upgrades permissions (MMU_NOTIFIER_RANGE_PERM_UPGRADE), keep the existing SPTEs instead of zapping them. The PFN is unchanged and no access is revoked, so a held SPTE is at most as permissive as before. Permissions for the SPTE are updated on the next fault, so dropping them early gains nothing. The motivating case is a userfaultfd-wp dirty tracker such as QEMU's background snapshot, which unprotects every guest page as it saves it. Zapping on each unprotect makes the guest refault its whole working set. On a 64GB guest under a background snapshot, a read-mostly workload drops secondary-MMU refaults from ~1M/s to ~2.5K/s and cross-vCPU TLB shootdowns from ~1400/s to near zero. Uses of mprotect() that only add access benefit likewise. Signed-off-by: Carlos López --- arch/x86/kvm/mmu/mmu.c | 7 +++++++ 1 file changed, 7 insertions(+) diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c index dc2aef72ffdd..a4258a8c0c89 100644 --- a/arch/x86/kvm/mmu/mmu.c +++ b/arch/x86/kvm/mmu/mmu.c @@ -1719,6 +1719,13 @@ bool kvm_unmap_gfn_range(struct kvm *kvm, struct kvm_gfn_range *range) lockdep_assert_once(kvm->mmu_invalidate_in_progress || lockdep_is_held(&kvm->slots_lock)); + /* + * Do not bother zapping SPTEs if this is only a protection upgrade. + * Permissions will be faulted-in on demand. + */ + if (range->perm_upgrade) + return false; + if (kvm_memslots_have_rmaps(kvm)) flush = __kvm_rmap_zap_gfn_range(kvm, range->slot, range->start, range->end, -- 2.51.0