From mboxrd@z Thu Jan 1 00:00:00 1970 From: Julien Grall Subject: Re: [PATCH] xen/arm: p2m: Restrict preemption check in apply_p2m_changes Date: Tue, 5 May 2015 17:31:01 +0100 Message-ID: <5548F045.1090506@citrix.com> References: <1430838129-21693-1-git-send-email-julien.grall@citrix.com> <20150505155041.GG31936@l.oracle.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: Received: from mail6.bemta5.messagelabs.com ([195.245.231.135]) by lists.xen.org with esmtp (Exim 4.72) (envelope-from ) id 1Ypfwi-0000K3-DL for xen-devel@lists.xenproject.org; Tue, 05 May 2015 16:43:48 +0000 In-Reply-To: <20150505155041.GG31936@l.oracle.com> List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xen.org Errors-To: xen-devel-bounces@lists.xen.org To: Konrad Rzeszutek Wilk Cc: ian.campbell@citrix.com, Riku Voipio , tim@xen.org, stefano.stabellini@citrix.com, xen-devel@lists.xenproject.org, Tamas K Lengyel List-Id: xen-devel@lists.xenproject.org Hi Konrad, On 05/05/15 16:50, Konrad Rzeszutek Wilk wrote: >> --- >> xen/arch/arm/p2m.c | 4 +++- >> 1 file changed, 3 insertions(+), 1 deletion(-) >> >> diff --git a/xen/arch/arm/p2m.c b/xen/arch/arm/p2m.c >> index 65efa94..59dd23a 100644 >> --- a/xen/arch/arm/p2m.c >> +++ b/xen/arch/arm/p2m.c >> @@ -948,6 +948,7 @@ static int apply_p2m_changes(struct domain *d, >> const unsigned long sgfn = paddr_to_pfn(start_gpaddr), >> egfn = paddr_to_pfn(end_gpaddr); >> const unsigned int preempt_count_limit = (op == MEMACCESS) ? 1 : 0x2000; >> + const bool_t preempt = !is_idle_vcpu(current); >> bool_t flush = false; >> bool_t flush_pt; >> >> @@ -980,7 +981,8 @@ static int apply_p2m_changes(struct domain *d, >> * always make at least one pass as long as preempt_count_limit is >> * initialized with a value >= 1. >> */ >> - if ( count >= preempt_count_limit && hypercall_preempt_check() ) >> + if ( preempt && count >= preempt_count_limit >> + && hypercall_preempt_check() ) > > Could you use the softirq_pending() check to deal when there are no domains? apply_p2m_changes will only be called with no current domain (i.e idle vcpu) during DOM0 construction. If we check softirq_pending for this case, you will Xen will fail to build DOM0 but the preemption is not supported. I suspect this is the same on x86. Regards, -- Julien Grall