Re: [Xen-devel] [RFC] xen/arm: Handling cache maintenance instructions by set/way

>>> On 11.12.17 at 21:26, wrote: > On 12/11/2017 10:06 AM, Jan Beulich wrote: > On 08.12.17 at 15:38, wrote: >>> On 08/12/17 08:03, Tim Deegan wrote: It should be possible to do something like the misconfigured-entry bit trick by

Re: [Xen-devel] [RFC] xen/arm: Handling cache maintenance instructions by set/way

On 12/11/2017 11:10 AM, Andre Przywara wrote: Hi, Hi Andre, But on the other hand we had PoD naturally already in KVM, so this came at no cost. So I believe it would be worth to investigate what the actual impact is on booting a 32-bit kernel, with emulating s/w ops like KVM does (see

Re: [Xen-devel] [RFC] xen/arm: Handling cache maintenance instructions by set/way

Hi Jan, On 12/11/2017 10:06 AM, Jan Beulich wrote: On 08.12.17 at 15:38, wrote: On 08/12/17 08:03, Tim Deegan wrote: It should be possible to do something like the misconfigured-entry bit trick by _allocating_ the memory up-front and building the p2m entries but only

Re: [Xen-devel] [RFC] xen/arm: Handling cache maintenance instructions by set/way

Hi, On 12/10/2017 03:22 PM, Tim Deegan wrote: At 14:38 + on 08 Dec (1512743913), Julien Grall wrote: On 08/12/17 08:03, Tim Deegan wrote: +1 for avoiding the full majesty of PoD if you don't need it. It should be possible to do something like the misconfigured-entry bit trick by

Re: [Xen-devel] [RFC] xen/arm: Handling cache maintenance instructions by set/way

At 14:38 + on 08 Dec (1512743913), Julien Grall wrote: > On 08/12/17 08:03, Tim Deegan wrote: > > +1 for avoiding the full majesty of PoD if you don't need it. > > > > It should be possible to do something like the misconfigured-entry bit > > trick by _allocating_ the memory up-front and

Re: [Xen-devel] [RFC] xen/arm: Handling cache maintenance instructions by set/way

On 08/12/17 08:03, Tim Deegan wrote: Hi, Hi Tim, Somehow your e-mail was marked as spam by gmail. At 12:58 + on 06 Dec (1512565090), Julien Grall wrote: On 12/06/2017 12:28 PM, George Dunlap wrote: 2. It sounds like rather than using PoD, you could use the "misconfigured p2m table"

Re: [Xen-devel] [RFC] xen/arm: Handling cache maintenance instructions by set/way

On 12/07/2017 07:21 PM, Marc Zyngier wrote: > On 07/12/17 18:06, George Dunlap wrote: >> On 12/07/2017 04:58 PM, Marc Zyngier wrote: >>> On 07/12/17 16:44, George Dunlap wrote: On 12/07/2017 04:04 PM, Julien Grall wrote: > Hi Jan, > > On 07/12/17 15:45, Jan Beulich wrote:

Re: [Xen-devel] [RFC] xen/arm: Handling cache maintenance instructions by set/way

Hi, At 12:58 + on 06 Dec (1512565090), Julien Grall wrote: > On 12/06/2017 12:28 PM, George Dunlap wrote: > > 2. It sounds like rather than using PoD, you could use the > > "misconfigured p2m table" technique that x86 uses: set bits in the p2m > > entry which cause a specific kind of HAP

Re: [Xen-devel] [RFC] xen/arm: Handling cache maintenance instructions by set/way

On 07/12/17 18:06, George Dunlap wrote: > On 12/07/2017 04:58 PM, Marc Zyngier wrote: >> On 07/12/17 16:44, George Dunlap wrote: >>> On 12/07/2017 04:04 PM, Julien Grall wrote: Hi Jan, On 07/12/17 15:45, Jan Beulich wrote: On 07.12.17 at 15:53, wrote:

Re: [Xen-devel] [RFC] xen/arm: Handling cache maintenance instructions by set/way

On 12/07/2017 04:58 PM, Marc Zyngier wrote: > On 07/12/17 16:44, George Dunlap wrote: >> On 12/07/2017 04:04 PM, Julien Grall wrote: >>> Hi Jan, >>> >>> On 07/12/17 15:45, Jan Beulich wrote: >>> On 07.12.17 at 15:53, wrote: > On 07/12/17 13:52, Julien Grall wrote:

Re: [Xen-devel] [RFC] xen/arm: Handling cache maintenance instructions by set/way

On 12/07/2017 04:04 PM, Julien Grall wrote: > Hi Jan, > > On 07/12/17 15:45, Jan Beulich wrote: > On 07.12.17 at 15:53, wrote: >>> On 07/12/17 13:52, Julien Grall wrote: >>> There is exactly one case where set/way makes sense, and that's when >>> you're the only CPU

Re: [Xen-devel] [RFC] xen/arm: Handling cache maintenance instructions by set/way

Hi Jan, On 07/12/17 15:45, Jan Beulich wrote: On 07.12.17 at 15:53, wrote: On 07/12/17 13:52, Julien Grall wrote: There is exactly one case where set/way makes sense, and that's when you're the only CPU left in the system, your MMU is off, and you're about to go down.

Re: [Xen-devel] [RFC] xen/arm: Handling cache maintenance instructions by set/way

>>> On 07.12.17 at 16:22, wrote: > On 07/12/17 09:39, Jan Beulich wrote: > On 06.12.17 at 18:52, wrote: >>> But I think this is bringing another class of problem. When a >>> misconfigured is accessed, we would need to clean & invalidate the

Re: [Xen-devel] [RFC] xen/arm: Handling cache maintenance instructions by set/way

(+ Marc) @Marc: My Arm cache knowledge is somewhat limited. Feel free to correct me if I am wrong. On 07/12/17 09:39, Jan Beulich wrote: On 06.12.17 at 18:52, wrote: On 12/06/2017 03:15 PM, Jan Beulich wrote: What we do in x86 is that we flag all entries at the

Re: [Xen-devel] [RFC] xen/arm: Handling cache maintenance instructions by set/way

On 07/12/17 13:52, Julien Grall wrote: > (+ Marc) > > Hi, > > @Marc: My Arm cache knowledge is somewhat limited. Feel free to correct > me if I am wrong. > > Before answering to the rest of the e-mail, let me reinforce what I said > in my first e-mail. Set/Way are very complex to emulate and

Re: [Xen-devel] [RFC] xen/arm: Handling cache maintenance instructions by set/way

>>> On 07.12.17 at 14:52, wrote: > On 06/12/17 17:49, George Dunlap wrote: >> Do you want to reset the p2m multiple times? I thought the goal was >> simply to keep the amount of p2m space you need to flush to a minimum; >> if you expect the memory which has been faulted

Re: [Xen-devel] [RFC] xen/arm: Handling cache maintenance instructions by set/way

(+ Marc) Hi, @Marc: My Arm cache knowledge is somewhat limited. Feel free to correct me if I am wrong. Before answering to the rest of the e-mail, let me reinforce what I said in my first e-mail. Set/Way are very complex to emulate and an OS using them should never expect good performance

Re: [Xen-devel] [RFC] xen/arm: Handling cache maintenance instructions by set/way

>>> On 06.12.17 at 18:52, wrote: > On 12/06/2017 03:15 PM, Jan Beulich wrote: >> What we do in x86 is that we flag all entries at the top level as >> misconfigured at any time where otherwise we would have to >> walk the full tree. Upon access, the misconfigured flag is

Re: [Xen-devel] [RFC] xen/arm: Handling cache maintenance instructions by set/way

On 12/06/2017 12:58 PM, Julien Grall wrote: > Hi George, > > On 12/06/2017 12:28 PM, George Dunlap wrote: >> On 12/05/2017 06:39 PM, Julien Grall wrote: >>> Hi all, >>> >>> Even though it is an Arm failure, I have CCed x86 folks to get feedback >>> on the approach. I have a WIP branch I could

Re: [Xen-devel] [RFC] xen/arm: Handling cache maintenance instructions by set/way

On 12/06/2017 03:24 PM, George Dunlap wrote: On 12/06/2017 03:19 PM, Julien Grall wrote: Hi Konrad, On 12/06/2017 03:10 PM, Konrad Rzeszutek Wilk wrote: .snip.. The suggested policy is based on the KVM one: - If we trap a S/W instructions, we enable VM trapping (e.g HCR_EL2.TVM) to

Re: [Xen-devel] [RFC] xen/arm: Handling cache maintenance instructions by set/way

On 12/06/2017 03:19 PM, Julien Grall wrote: > Hi Konrad, > > On 12/06/2017 03:10 PM, Konrad Rzeszutek Wilk wrote: >> .snip.. >>> The suggested policy is based on the KVM one: >>> - If we trap a S/W instructions, we enable VM trapping (e.g >>> HCR_EL2.TVM) to >>> detect cache being turned

Re: [Xen-devel] [RFC] xen/arm: Handling cache maintenance instructions by set/way

Hi Konrad, On 12/06/2017 03:10 PM, Konrad Rzeszutek Wilk wrote: .snip.. The suggested policy is based on the KVM one: - If we trap a S/W instructions, we enable VM trapping (e.g HCR_EL2.TVM) to detect cache being turned on/off, and do a full clean. - We flush the caches on

Re: [Xen-devel] [RFC] xen/arm: Handling cache maintenance instructions by set/way

>>> On 06.12.17 at 13:58, wrote: > On 12/06/2017 12:28 PM, George Dunlap wrote: >> 2. It sounds like rather than using PoD, you could use the >> "misconfigured p2m table" technique that x86 uses: set bits in the p2m >> entry which cause a specific kind of HAP fault when

Re: [Xen-devel] [RFC] xen/arm: Handling cache maintenance instructions by set/way

.snip.. > The suggested policy is based on the KVM one: > - If we trap a S/W instructions, we enable VM trapping (e.g > HCR_EL2.TVM) to > detect cache being turned on/off, and do a full clean. > - We flush the caches on both caches being turned on and off. > - Once the caches

Re: [Xen-devel] [RFC] xen/arm: Handling cache maintenance instructions by set/way

On 12/06/2017 12:58 PM, Julien Grall wrote: Hi George, On 12/06/2017 12:28 PM, George Dunlap wrote: On 12/05/2017 06:39 PM, Julien Grall wrote: Hi all, Even though it is an Arm failure, I have CCed x86 folks to get feedback on the approach. I have a WIP branch I could share if that

Re: [Xen-devel] [RFC] xen/arm: Handling cache maintenance instructions by set/way

Hi George, On 12/06/2017 12:28 PM, George Dunlap wrote: On 12/05/2017 06:39 PM, Julien Grall wrote: Hi all, Even though it is an Arm failure, I have CCed x86 folks to get feedback on the approach. I have a WIP branch I could share if that interest people. Few months ago, we noticed an

Re: [Xen-devel] [RFC] xen/arm: Handling cache maintenance instructions by set/way

On 12/05/2017 06:39 PM, Julien Grall wrote: > Hi all, > > Even though it is an Arm failure, I have CCed x86 folks to get feedback > on the approach. I have a WIP branch I could share if that interest people. > > Few months ago, we noticed an heisenbug on jobs run by osstest on the > cubietrucks

Re: [Xen-devel] [RFC] xen/arm: Handling cache maintenance instructions by set/way

Hi Jan, On 12/06/2017 09:15 AM, Jan Beulich wrote: On 05.12.17 at 19:39, wrote: The suggested policy is based on the KVM one: - If we trap a S/W instructions, we enable VM trapping (e.g HCR_EL2.TVM) to detect cache being turned on/off, and do a full clean.

Re: [Xen-devel] [RFC] xen/arm: Handling cache maintenance instructions by set/way

>>> On 05.12.17 at 19:39, wrote: > The suggested policy is based on the KVM one: > - If we trap a S/W instructions, we enable VM trapping (e.g > HCR_EL2.TVM) to detect cache being turned on/off, and do a full clean. > - We flush the caches on both caches

Re: [Xen-devel] [RFC] xen/arm: Handling cache maintenance instructions by set/way

On 05/12/2017 22:35, Stefano Stabellini wrote: On Tue, 5 Dec 2017, Julien Grall wrote: Hi all, Even though it is an Arm failure, I have CCed x86 folks to get feedback on the approach. I have a WIP branch I could share if that interest people. Few months ago, we noticed an heisenbug on jobs

Re: [Xen-devel] [RFC] xen/arm: Handling cache maintenance instructions by set/way

On Tue, 5 Dec 2017, Julien Grall wrote: > Hi all, > > Even though it is an Arm failure, I have CCed x86 folks to get feedback on the > approach. I have a WIP branch I could share if that interest people. > > Few months ago, we noticed an heisenbug on jobs run by osstest on the > cubietrucks (see

[Xen-devel] [RFC] xen/arm: Handling cache maintenance instructions by set/way

Hi all, Even though it is an Arm failure, I have CCed x86 folks to get feedback on the approach. I have a WIP branch I could share if that interest people. Few months ago, we noticed an heisenbug on jobs run by osstest on the cubietrucks (see [1]). From the log, we figured out that the guest