From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Google-Smtp-Source: AH8x225ijWFEPNZqmXFwaaqLsP+3rE8iDaaBKNE05r6fWATtgjley4mAVP+aV08Yd5RmOOrG2Z8H ARC-Seal: i=1; a=rsa-sha256; t=1518708815; cv=none; d=google.com; s=arc-20160816; b=vqG0YPOllwA62O1f2gdzxqZ+kdSdhg5EAqnAHqMH40n7wX3GRoXP3PDzK5lOKIVHvD gBq8jJNjsPMeDZn5rNMUTj9aN8pDU7jyW+QkdOAYWyn8FpMepG4FJEHyc3ESdO9PQD+H +WEGUS1ImZKZCv8DLw+9YM3vA9+/p0VRg92S88sFGzO5c7EUkP2fS7ivLjXlU1OET3Qh zl3vHO3k2m9JbGy7sQ0MCmhWkbnoeDMOONiK0bZc6suajedfETvZCxSlHK1yJKEE6XuC tYsYuxTpCqyPwU3lvn8eOKi1TfhbIXWCD8zm0k5fzqzmmPa7LjFq/7YF+MUuMsiOnLdL xtFQ== ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=arc-20160816; h=mime-version:user-agent:references:in-reply-to:message-id:date :subject:cc:to:from:arc-authentication-results; bh=lmUvg6EibFIPLn8uztA8rYxVesKAddpu+kvGDCbyQpQ=; b=ruJohljKQtSo0tgA1iYCi1BHmjvVXmceRSGHgOraUS0OD4WzbOdbAgMzuAVUYydeie 05MmpdXwhCEjjOlcGwgeiPU6zXtrkmQJTbsuDg29sQjYDV71AOL7/kyWIv8S9iXYPfkw TJdQ7XmnEccQacwrtG5N2gZO6KCEdODBbxXnJIlVAzJIyjpj3pJ3R6vBxZa12N7lbVtq VyjB0Pj0WxsZd9sEFXRo1blZpcUpwzlMpv9b+7P16McXNLui6CSxupKFAHsH/0qLCrDI VsFl8+teG0WnjEcLD/SiX5I7l9xN2uaOQlXIXJkoS4H/SJ5DpDUj4PASea+BjICJE1Hc hd9A== ARC-Authentication-Results: i=1; mx.google.com; spf=softfail (google.com: domain of transitioning gregkh@linuxfoundation.org does not designate 90.92.71.90 as permitted sender) smtp.mailfrom=gregkh@linuxfoundation.org Authentication-Results: mx.google.com; spf=softfail (google.com: domain of transitioning gregkh@linuxfoundation.org does not designate 90.92.71.90 as permitted sender) smtp.mailfrom=gregkh@linuxfoundation.org From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Will Deacon , Catalin Marinas , Ard Biesheuvel Subject: [PATCH 4.14 054/195] [Variant 3/Meltdown] arm64: entry: Reword comment about post_ttbr_update_workaround Date: Thu, 15 Feb 2018 16:15:45 +0100 Message-Id: <20180215151708.438842785@linuxfoundation.org> X-Mailer: git-send-email 2.16.1 In-Reply-To: <20180215151705.738773577@linuxfoundation.org> References: <20180215151705.738773577@linuxfoundation.org> User-Agent: quilt/0.65 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 X-getmail-retrieved-from-mailbox: INBOX X-GMAIL-LABELS: =?utf-8?b?IlxcU2VudCI=?= X-GMAIL-THRID: =?utf-8?q?1592481614830808398?= X-GMAIL-MSGID: =?utf-8?q?1592481614830808398?= X-Mailing-List: linux-kernel@vger.kernel.org List-ID: 4.14-stable review patch. If anyone has any objections, please let me know. ------------------ From: Will Deacon Commit f167211a93ac upstream. We don't fully understand the Cavium ThunderX erratum, but it appears that mapping the kernel as nG can lead to horrible consequences such as attempting to execute userspace from kernel context. Since kpti isn't enabled for these CPUs anyway, simplify the comment justifying the lack of post_ttbr_update_workaround in the exception trampoline. Signed-off-by: Will Deacon Signed-off-by: Catalin Marinas Signed-off-by: Ard Biesheuvel Signed-off-by: Greg Kroah-Hartman --- arch/arm64/kernel/entry.S | 13 +++---------- 1 file changed, 3 insertions(+), 10 deletions(-) --- a/arch/arm64/kernel/entry.S +++ b/arch/arm64/kernel/entry.S @@ -962,16 +962,9 @@ alternative_else_nop_endif orr \tmp, \tmp, #USER_ASID_FLAG msr ttbr1_el1, \tmp /* - * We avoid running the post_ttbr_update_workaround here because the - * user and kernel ASIDs don't have conflicting mappings, so any - * "blessing" as described in: - * - * http://lkml.kernel.org/r/56BB848A.6060603@caviumnetworks.com - * - * will not hurt correctness. Whilst this may partially defeat the - * point of using split ASIDs in the first place, it avoids - * the hit of invalidating the entire I-cache on every return to - * userspace. + * We avoid running the post_ttbr_update_workaround here because + * it's only needed by Cavium ThunderX, which requires KPTI to be + * disabled. */ .endm