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Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=noisy.programming.kicks-ass.net) by bombadil.infradead.org with esmtpsa (Exim 4.92.3 #3 (Red Hat Linux)) id 1jkttx-000598-1L; Mon, 15 Jun 2020 18:32:09 +0000 Received: from hirez.programming.kicks-ass.net (hirez.programming.kicks-ass.net [192.168.1.225]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (Client did not present a certificate) by noisy.programming.kicks-ass.net (Postfix) with ESMTPS id C7A7430604B; Mon, 15 Jun 2020 20:32:04 +0200 (CEST) Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id B5E05203DCA15; Mon, 15 Jun 2020 20:32:04 +0200 (CEST) Date: Mon, 15 Jun 2020 20:32:04 +0200 From: Peter Zijlstra To: "Raj, Ashok" Subject: Re: [PATCH v2 12/12] x86/traps: Fix up invalid PASID Message-ID: <20200615183204.GE2531@hirez.programming.kicks-ass.net> References: <1592008893-9388-1-git-send-email-fenghua.yu@intel.com> <1592008893-9388-13-git-send-email-fenghua.yu@intel.com> <20200615075649.GK2497@hirez.programming.kicks-ass.net> <20200615154854.GB13792@romley-ivt3.sc.intel.com> <20200615160357.GA2531@hirez.programming.kicks-ass.net> <20200615181921.GA33928@otc-nc-03> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <20200615181921.GA33928@otc-nc-03> Cc: Ravi V Shankar , Dave Hansen , H Peter Anvin , Dave Jiang , x86 , amd-gfx , Ingo Molnar , Fenghua Yu , Yu-cheng Yu , Andrew Donnellan , Borislav Petkov , Thomas Gleixner , Tony Luck , linuxppc-dev , Felix Kuehling , linux-kernel , iommu@lists.linux-foundation.org, Jacob Jun Pan , Frederic Barrat , David Woodhouse X-BeenThere: iommu@lists.linux-foundation.org X-Mailman-Version: 2.1.15 Precedence: list List-Id: Development issues for Linux IOMMU support List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Errors-To: iommu-bounces@lists.linux-foundation.org Sender: "iommu" On Mon, Jun 15, 2020 at 11:19:21AM -0700, Raj, Ashok wrote: > On Mon, Jun 15, 2020 at 06:03:57PM +0200, Peter Zijlstra wrote: > > > > I don't get why you need a rdmsr here, or why not having one would > > require a TIF flag. Is that because this MSR is XSAVE/XRSTOR managed? > > > > > > > + */ > > > > > + rdmsrl(MSR_IA32_PASID, pasid_msr); > > > > > + if (pasid_msr & MSR_IA32_PASID_VALID) > > > > > + return false; > > > > > + > > > > > + /* Fix up the MSR if the MSR doesn't have a valid PASID. */ > > > > > + wrmsrl(MSR_IA32_PASID, pasid | MSR_IA32_PASID_VALID); > > > > How much more expensive is the wrmsr over the rdmsr? Can't we just > > unconditionally write the current PASID and call it a day? > > The reason to check the rdmsr() is because we are using a hueristic taking > GP faults. If we already setup the MSR, but we get it a second time it > means the reason is something other than PASID_MSR not being set. > > Ideally we should use the TIF_ to track this would be cheaper, but we were > told those bits aren't easy to give out. Why do you need a TIF flag? Why not any other random flag in current? _______________________________________________ iommu mailing list iommu@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/iommu