Re: [PATCH v2 12/12] x86/traps: Fix up invalid PASID

2020-06-17 Thread Peter Zijlstra
On Tue, Jun 16, 2020 at 04:23:46PM -0700, Fenghua Yu wrote: > Hi, Peter, > > On Mon, Jun 15, 2020 at 09:09:28PM +0200, Peter Zijlstra wrote: > > On Mon, Jun 15, 2020 at 11:55:29AM -0700, Fenghua Yu wrote: > > > > > Or do you suggest to add a random new flag in struct thread_info instead > > > of

Re: [PATCH v2 12/12] x86/traps: Fix up invalid PASID

2020-06-16 Thread Fenghua Yu
Hi, Peter, On Mon, Jun 15, 2020 at 09:09:28PM +0200, Peter Zijlstra wrote: > On Mon, Jun 15, 2020 at 11:55:29AM -0700, Fenghua Yu wrote: > > > Or do you suggest to add a random new flag in struct thread_info instead > > of a TIF flag? > > Why thread_info? What's wrong with something simple like

Re: [PATCH v2 12/12] x86/traps: Fix up invalid PASID

2020-06-15 Thread Raj, Ashok
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); > > > > +

Re: [PATCH v2 12/12] x86/traps: Fix up invalid PASID

2020-06-15 Thread Peter Zijlstra
On Mon, Jun 15, 2020 at 01:17:35PM -0700, Fenghua Yu wrote: > Hi, Peter, > > On Mon, Jun 15, 2020 at 09:09:28PM +0200, Peter Zijlstra wrote: > > On Mon, Jun 15, 2020 at 11:55:29AM -0700, Fenghua Yu wrote: > > > > > Or do you suggest to add a random new flag in struct thread_info instead > > > of

RE: [PATCH v2 12/12] x86/traps: Fix up invalid PASID

2020-06-15 Thread Luck, Tony
> So what’s the RDMSR for? Surely you > have some state somewhere that says “this task has a PASID.” > Can’t you just make sure that stays in sync with the MSR? Then, on #GP, if > the task already has a PASID, you know the MSR is set. We have state that says the process ("mm") has been

Re: [PATCH v2 12/12] x86/traps: Fix up invalid PASID

2020-06-15 Thread Andy Lutomirski
> On Jun 15, 2020, at 1:56 PM, Luck, Tony wrote: > >  >> >> Are we planning to keep PASID live once a task has used it once or are we >> going to swap it lazily? If the latter, a percpu variable might be better. > > Current plan is "touch it once and the task owns it until exit(2)" > >

RE: [PATCH v2 12/12] x86/traps: Fix up invalid PASID

2020-06-15 Thread Luck, Tony
> Are we planning to keep PASID live once a task has used it once or are we > going to swap it lazily? If the latter, a percpu variable might be better. Current plan is "touch it once and the task owns it until exit(2)" Maybe someday in the future when we have data on how applications actually

Re: [PATCH v2 12/12] x86/traps: Fix up invalid PASID

2020-06-15 Thread Andy Lutomirski
> On Jun 15, 2020, at 1:17 PM, Fenghua Yu wrote: > > Hi, Peter, > >> On Mon, Jun 15, 2020 at 09:09:28PM +0200, Peter Zijlstra wrote: >>> On Mon, Jun 15, 2020 at 11:55:29AM -0700, Fenghua Yu wrote: >>> >>> Or do you suggest to add a random new flag in struct thread_info instead >>> of a TIF

Re: [PATCH v2 12/12] x86/traps: Fix up invalid PASID

2020-06-15 Thread Fenghua Yu
Hi, Peter, On Mon, Jun 15, 2020 at 09:09:28PM +0200, Peter Zijlstra wrote: > On Mon, Jun 15, 2020 at 11:55:29AM -0700, Fenghua Yu wrote: > > > Or do you suggest to add a random new flag in struct thread_info instead > > of a TIF flag? > > Why thread_info? What's wrong with something simple like

Re: [PATCH v2 12/12] x86/traps: Fix up invalid PASID

2020-06-15 Thread Peter Zijlstra
On Mon, Jun 15, 2020 at 11:55:29AM -0700, Fenghua Yu wrote: > Or do you suggest to add a random new flag in struct thread_info instead > of a TIF flag? Why thread_info? What's wrong with something simple like the below. It takes a bit from the 'strictly current' flags word. diff --git

Re: [PATCH v2 12/12] x86/traps: Fix up invalid PASID

2020-06-15 Thread Fenghua Yu
Hi, Peter, On Mon, Jun 15, 2020 at 08:31:16PM +0200, Peter Zijlstra wrote: > On Mon, Jun 15, 2020 at 11:12:59AM -0700, Fenghua Yu 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? > > > > My

Re: [PATCH v2 12/12] x86/traps: Fix up invalid PASID

2020-06-15 Thread Peter Zijlstra
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? > > > > > > > +

Re: [PATCH v2 12/12] x86/traps: Fix up invalid PASID

2020-06-15 Thread Peter Zijlstra
On Mon, Jun 15, 2020 at 11:12:59AM -0700, Fenghua Yu 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? > > My concern is TIF flags are precious (only 3 slots available). Defining > a new TIF flag

Re: [PATCH v2 12/12] x86/traps: Fix up invalid PASID

2020-06-15 Thread Fenghua Yu
On Mon, Jun 15, 2020 at 06:03:57PM +0200, Peter Zijlstra wrote: > On Mon, Jun 15, 2020 at 08:48:54AM -0700, Fenghua Yu wrote: > > Hi, Peter, > > On Mon, Jun 15, 2020 at 09:56:49AM +0200, Peter Zijlstra wrote: > > > On Fri, Jun 12, 2020 at 05:41:33PM -0700, Fenghua Yu wrote: > > > > +/* > > > > + *

RE: [PATCH v2 12/12] x86/traps: Fix up invalid PASID

2020-06-15 Thread Luck, Tony
>> The heuristic always initializes the MSR with the per mm PASID IIF the >> mm has a valid PASID but the MSR doesn't have one. This heuristic usually >> happens only once on the first #GP in a thread. > > But it doesn't guarantee the PASID is the right one. Suppose both the mm > has a PASID and

Re: [PATCH v2 12/12] x86/traps: Fix up invalid PASID

2020-06-15 Thread Peter Zijlstra
On Mon, Jun 15, 2020 at 08:48:54AM -0700, Fenghua Yu wrote: > Hi, Peter, > On Mon, Jun 15, 2020 at 09:56:49AM +0200, Peter Zijlstra wrote: > > On Fri, Jun 12, 2020 at 05:41:33PM -0700, Fenghua Yu wrote: > > > +/* > > > + * Apply some heuristics to see if the #GP fault was caused by a thread > > >

Re: [PATCH v2 12/12] x86/traps: Fix up invalid PASID

2020-06-15 Thread Fenghua Yu
Hi, Peter, On Mon, Jun 15, 2020 at 09:56:49AM +0200, Peter Zijlstra wrote: > On Fri, Jun 12, 2020 at 05:41:33PM -0700, Fenghua Yu wrote: > > +/* > > + * Apply some heuristics to see if the #GP fault was caused by a thread > > + * that hasn't had the IA32_PASID MSR initialized. If it looks like

Re: [PATCH v2 12/12] x86/traps: Fix up invalid PASID

2020-06-15 Thread Peter Zijlstra
On Fri, Jun 12, 2020 at 05:41:33PM -0700, Fenghua Yu wrote: > +/* > + * Apply some heuristics to see if the #GP fault was caused by a thread > + * that hasn't had the IA32_PASID MSR initialized. If it looks like that > + * is the problem, try initializing the IA32_PASID MSR. If the heuristic > +

Re: [PATCH v2 12/12] x86/traps: Fix up invalid PASID

2020-06-15 Thread Peter Zijlstra
On Fri, Jun 12, 2020 at 05:41:33PM -0700, Fenghua Yu wrote: > @@ -447,6 +458,18 @@ dotraplinkage void do_general_protection(struct pt_regs > *regs, long error_code) > int ret; > > RCU_LOCKDEP_WARN(!rcu_is_watching(), "entry code didn't wake RCU"); > + > + /* > + * Perform