From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Google-Smtp-Source: AH8x2254nLE+CokZw1k6bd3/TnPJ/oJhgi0dvbkcYffhQgcqeEE9nxV4V3JK2AN0mcq63+KoWX7R ARC-Seal: i=1; a=rsa-sha256; t=1516645765; cv=none; d=google.com; s=arc-20160816; b=uXrn3a4Lrzz0iUvIzjiq0JSzWzfZLyQmlQxHxdnDXQmVDXbiz+lAUWdjwMvqQSYbsc pwDVbRq0dahFEIft0Dl6I5ywn2H6yaUsdlCiGjmOIBaIYFzzRRJ869vlY4FIaPstzuTW p45qDZOooH9fPo4XoJFIYlA43EaB9+aD3gF0ND4QAPeWHv3TS16n2/NTuhEVB1MqP6dh CPNXwIHWfYXY0al3jpduaxGophR0dzpYqTwJZLFRgq7dTI3m0G0TI9k4JhfoMS//Jz4L y2T2MY3X0XV/BQI4Iv/6jF/DEcm5MaFgFjMQFM9HAwyhXrECqiPvsvXy8tDfH5iTjBqA RinQ== ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=arc-20160816; h=content-transfer-encoding:content-language:in-reply-to:mime-version :user-agent:date:message-id:from:references:cc:to:subject :arc-authentication-results; bh=vczQv8f+XVItok2jJaFpkcCI+iKIRu3xItrmjcRlGXc=; b=YRLF3GKy85sHRMet7ckgxjimPU6CsH/s1eVV3ROeLnWuJj8PURRZWT0PbUEWgqg4NF ZjT8bt6kJapV/Eht3GmIOE1JdNtMIO7hHFSWYhYohCh61ntJKO81WkttArMT2YkYZ51U gkw+FYJY8SO1cfbvBiqPPiZq5Emlc21fMfw7WsgAODFBXJpdTE9zwNXSw4M6VofUvGzl rFQ+wCm6cQ/XZIz+EwdRh51HCbcMMJdqE3/ddbAU+WEYqNwznmtO9MmRqeohd8PYf6Ew I+/xdFL2i00K90AFPklH4orCBDg7N5o5CZFzhSmjpFSAyqejeVQgkv0Kb45Nlot1KkHk l4Sg== ARC-Authentication-Results: i=1; mx.google.com; spf=pass (google.com: best guess record for domain of tim.c.chen@linux.intel.com designates 192.55.52.88 as permitted sender) smtp.mailfrom=tim.c.chen@linux.intel.com Authentication-Results: mx.google.com; spf=pass (google.com: best guess record for domain of tim.c.chen@linux.intel.com designates 192.55.52.88 as permitted sender) smtp.mailfrom=tim.c.chen@linux.intel.com X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.46,397,1511856000"; d="scan'208";a="12562247" Subject: Re: [RFC 04/10] x86/mm: Only flush indirect branches when switching into non dumpable process To: "Woodhouse, David" , KarimAllah Ahmed , linux-kernel@vger.kernel.org Cc: Andi Kleen , Andrea Arcangeli , Andy Lutomirski , Arjan van de Ven , Ashok Raj , Asit Mallick , Borislav Petkov , Dan Williams , Dave Hansen , Greg Kroah-Hartman , "H . Peter Anvin" , Ingo Molnar , Janakarajan Natarajan , Joerg Roedel , Jun Nakajima , Laura Abbott , Linus Torvalds , Masami Hiramatsu , Paolo Bonzini , Peter Zijlstra , =?UTF-8?B?UmFkaW0gS3LEjW3DocWZ?= , Thomas Gleixner , Tom Lendacky , kvm@vger.kernel.org, x86@kernel.org References: <1516476182-5153-1-git-send-email-karahmed@amazon.de> <1516476182-5153-5-git-send-email-karahmed@amazon.de> <1516482364.9814.18.camel@amazon.co.uk> From: Tim Chen Message-ID: Date: Mon, 22 Jan 2018 10:29:23 -0800 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.1.0 MIME-Version: 1.0 In-Reply-To: <1516482364.9814.18.camel@amazon.co.uk> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit X-getmail-retrieved-from-mailbox: INBOX X-GMAIL-THRID: =?utf-8?q?1590140567714479425?= X-GMAIL-MSGID: =?utf-8?q?1590318349892964122?= X-Mailing-List: linux-kernel@vger.kernel.org List-ID: On 01/20/2018 01:06 PM, Woodhouse, David wrote: > On Sat, 2018-01-20 at 20:22 +0100, KarimAllah Ahmed wrote: >> From: Tim Chen > > I think this is probably From: Andi now rather than From: Tim? This change is from Andi. >> 1 file changed, 12 insertions(+), 1 deletion(-) >> >> diff --git a/arch/x86/mm/tlb.c b/arch/x86/mm/tlb.c >> index 304de7d..f64e80c 100644 >> --- a/arch/x86/mm/tlb.c >> +++ b/arch/x86/mm/tlb.c >> @@ -225,8 +225,19 @@ void switch_mm_irqs_off(struct mm_struct *prev, struct mm_struct *next, >> * Avoid user/user BTB poisoning by flushing the branch predictor >> * when switching between processes. This stops one process from >> * doing Spectre-v2 attacks on another. >> + * >> + * As an optimization: Flush indirect branches only when >> + * switching into processes that disable dumping. >> + * >> + * This will not flush when switching into kernel threads. >> + * But it would flush when switching into idle and back >> + * >> + * It might be useful to have a one-off cache here >> + * to also not flush the idle case, but we would need some >> + * kind of stable sequence number to remember the previous mm. >> */ >> - indirect_branch_prediction_barrier(); >> + if (tsk && tsk->mm && get_dumpable(tsk->mm) != SUID_DUMP_USER) >> + indirect_branch_prediction_barrier(); We could move this close to the cr3 write. The cr3 write provides barrier against unwanted speculation in the above if check. Tim