From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (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 9BEFD606A31A for ; Thu, 29 Oct 2026 08:54:33 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key, unprotected) header.d=lists.infradead.org header.i=@lists.infradead.org header.a=rsa-sha256 header.s=bombadil.20210309 header.b=DPUCDeBE; dkim=pass (1024-bit key, unprotected) header.d=linux.dev header.i=@linux.dev header.a=rsa-sha256 header.s=key1 header.b=eff/UEkS DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender:List-Subscribe:List-Help :List-Post:List-Archive:List-Unsubscribe:List-Id:Content-Transfer-Encoding: MIME-Version:References:In-Reply-To:Message-ID:Date:Subject:Cc:To:From: Reply-To:Content-Type:Content-ID:Content-Description:Resent-Date:Resent-From: Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Unsubscribe-Post: List-Owner; bh=kpm89XioXXnsTWzJsIlmeTzj5KiGn1VrgU9z1qz9vOk=; b=DPUCDeBEbDQvqo 7THdMiS0p82/tklap64tbnXRD5LkCPtgqWbfYtAXRrWAw+G/kOiAAJv6NFsF7IzlyErlF/AXZvAjc MErhDCm001/3cXjG9NVRsDydeIENzJiU0fGRErNXzQ5yW89x7BSnqOrYfzkXj/HAhLJhAZcsBdkee PXOczte2v9YzNMcCybnKncRjrrNNv6TC/VGB59CBeSwVV5CCnhVVwaaTaH6pebG6OP32mvldKdX5v Be4gJWNaTFb1j9kJEoh+tqWlgGxr5hLZQLws/hM07ThPiRG6l3UYfgyBZucjBphR6dbfxP1IMJ9iZ bO5xS9sjOMVvtbqg66ow==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.100.1 #2 (Red Hat Linux)) id 1xMLtz-00000008ltO-0V6e; Thu, 29 Oct 2026 08:54:27 +0000 Received: from out-143.mta1.migadu.com ([95.215.58.143] helo=mta1.migadu.com) by bombadil.infradead.org with esmtps (Exim 4.100.1 #2 (Red Hat Linux)) id 1xMLtv-00000008lso-0CRg for linux-arm-kernel@lists.infradead.org; Thu, 29 Oct 2026 08:54:26 +0000 X-Envelope-To: linux-arm-kernel@lists.infradead.org DKIM-Signature: a=rsa-sha256; bh=ctrBwXQvS1M9yecPf1fWtqcUruy7KRm5Qjr3D6oimXs=; c=simple/simple; d=linux.dev; h=from:to:subject:date:message-id:mime-version:content-type; s=key1; t=1793264060; v=1; x=1793868860; b=eff/UEkSgCt3RsVBav8UPUofePVEzgdIjPSZ3BT9y+e48I6KvqNEyKUd1hiRAJT9mpQenVeU PPzbLB0BBip6x06BBdkis5xmRzqwIEjQ2w3jX3wMHvYwyDsFC075ceyRjTcehEO0KI9Mayd74e5 CclxNeni8WI0VW9Kh3vjYKEk= X-Envelope-To: linux-arm-kernel@lists.infradead.org Received: by smtp.migadu.com with ESMTPS id 615dd020fd29c127; Thu, 29 Oct 2026 08:54:20 +0000 X-Mizu-Trace-ID: 615dd020fd29c127 X-Migadu-Flow: FLOW_OUT From: Fuad Tabba To: xuheng@cs.columbia.edu Cc: maz@kernel.org, oupton@kernel.org, qperret@google.com, will@kernel.org, catalin.marinas@arm.com, mark.rutland@arm.com, joey.gouly@arm.com, seiden@linux.ibm.com, suzuki.poulose@arm.com, yuzenghui@huawei.com, kvmarm@lists.linux.dev, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, tabba@google.com Subject: Re: [PATCH] KVM: arm64: Add an ISB after mapping a hyp fixmap slot Date: Thu, 29 Oct 2026 08:54:14 +0000 Message-ID: <20261029085414.2279900-1-fuad.tabba@linux.dev> X-Mailer: git-send-email 2.47.3 In-Reply-To: <20261028-fixmap-isb-v1-1-6c9f0f9cb810@cs.columbia.edu> References: <20261028-fixmap-isb-v1-1-6c9f0f9cb810@cs.columbia.edu> X-Archived-By: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.9.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20261029_015423_545158_C8B2D01E X-CRM114-Status: UNSURE ( 8.50 ) X-CRM114-Notice: Please train this message. X-Spam-Score: -2.8 (--) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" X-Spam-Status: No, score=-13.9 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS,USER_AGENT_GIT autolearn=ham autolearn_force=no version=4.0.1 X-Spam-Checker-Version: SpamAssassin 4.0.1 (2024-03-26) on aws-us-west-2-korg-listserv-alma10-1 Hi Xuheng, On Wed, 28 Oct 2026 23:02:10 +0000, Xuheng Li wrote: [...] > A litmus test of the same shape (map the slot, DSB ISHST, load through > it) faulted on a Cortex-A72 in 2 out of 100M runs. Arm's herd7 model > with -variant vmsa also allows the fault, and forbids it once the ISB > is added. nit: it would help to have the litmus test itself in the commit message, or as a commit note, so the herd7 claim can be checked. Here's the one I ran (herd7 7.58, -variant vmsa): "Sometimes" as below, "Never" with an ISB after the DSB, and "Never" without the ISB under -variant vmsa,ETS2. AArch64 fixmap-noisb { [PTE(x)]=(oa:PA(x), valid:0); 0:X1=PTE(x); 0:X2=(oa:PA(x)); 0:X3=x; } P0 ; STR X2,[X1] ; DSB ISHST ; LDR W4,[X3] ; exists (fault(P0,x)) FWIW, the result matches the ARM ARM (B2.3: without FEAT_ETS2, a DSB ST doesn't order an earlier store before a later translation table walk), and emit_pte_barriers() in arch/arm64/include/asm/pgtable.h has the same dsb(ishst) plus isb() after making a kernel pte valid, for the same reason. [...] Reviewed-by: Fuad Tabba Tested in protected mode on QEMU, booting a protected and a non-protected guest, and on an Apple M4 (nested virtualization), booting a protected guest. No regressions. Tested-by: Fuad Tabba Cheers, /fuad