From: Corneliu ZUZU <czuzu@bitdefender.com> To: Julien Grall <julien.grall@arm.com>, xen-devel@lists.xen.org Cc: Andre Przywara <andre.przywara@arm.com>, Stefano Stabellini <sstabellini@kernel.org>, Tamas K Lengyel <tamas@tklengyel.com>, Razvan Cojocaru <rcojocaru@bitdefender.com>, Steve Capper <Steve.Capper@arm.com> Subject: Re: [PATCH 7/7] vm-event/arm: implement support for control-register write vm-events Date: Fri, 24 Jun 2016 12:32:48 +0300 [thread overview] Message-ID: <94545ef5-d527-5f23-83be-ca81ed966575@bitdefender.com> (raw) In-Reply-To: <576BC3E1.1080707@arm.com> On 6/23/2016 2:11 PM, Julien Grall wrote: > Hello, > > On 23/06/16 06:49, Corneliu ZUZU wrote: >> On 6/23/2016 8:31 AM, Corneliu ZUZU wrote: >>> On 6/22/2016 10:41 PM, Julien Grall wrote: >>>> >>>> >>>> On 22/06/2016 20:37, Corneliu ZUZU wrote: >>>>> I've also realized that it's a bit complicated to avoid writing HCR >>>>> from >>>>> 2 places. >>>>> That's because: >>>>> - p2m_restore_state is part of the process of switching to another >>>>> vCPU >>>>> and the HCR write _must be committed_ here because other components >>>>> depend on that, like address-translation functions >>>>> - I want vm_event_vcpu_enter to be called _after_ the switch to the >>>>> vCPU >>>>> is completed >>>>> - I want HCR_TVM to be set in vm_event_vcpu_enter because setting >>>>> necessary traps _for cr vm-events_ to work should be done there >>>>> (setting >>>>> HCR_TVM bit makes sense to be there and the purpose is to centralize >>>>> operations such as this for code comprehensibility; also, on the X86 >>>>> counterpart a similar operation is done for trapping CR3, so it >>>>> would be >>>>> nice to keep the symmetry) >>>>> >>>>> Would it be such a stretch to have HCR written in 2 places? (the >>>>> second >>>>> time happens rarely anyway: it's unlikely(..) to have to do the >>>>> write in >>>>> vm_event_vcpu_enter) >>>> >>>> Not really. It was mostly to avoid setting/clearing HCR bits in >>>> different place in the code. It makes more difficult to know what is >>>> the final result of the register. >>>> >>>> Anyway, let's skip it for now, if it is too difficult. >>>> >>>> Regards, >>>> >>> >>> Then perhaps something like the following would be suitable: >>> >>> 1. store hcr in arch_domain (register_t hcr) >>> >>> 2. add a function in asm-arm/processor.h (or where else?) which only >>> does: >>> static inline void update_hcr(struct domain *d) >>> { >>> WRITE_SYSREG(d->arch.hcr, HCR_EL2); >>> isb(); >>> } >>> >>> 3. modify p2m_restore_state to do: >>> n->domain->arch.hcr &= ~HCR_VM; >>> update_hcr(n->domain); >>> p2m_load_VTTBR(n->domain); >>> >>> n->domain->arch.hcr |= HCR_VM; >>> >>> if ( is_32bit_domain(n->domain) ) >>> n->domain->arch.hcr &= ~HCR_RW; >>> else >>> n->domain->arch.hcr |= HCR_RW; > > This is not safe at all, p2m_restore_state is vCPU specific at you > modify domain information. > > However, if we store the hcr per domain, overriding every context > switch is pointless as the domain will always be 32-bit/64-bit. Oh right, the RW bit needs not be set/unset anymore with this change. > >>> >>> update_hcr(n->domain); >>> >>> WRITE_SYSREG(n->arch.sctlr, SCTLR_EL1); >>> isb(); >>> >>> 4. and vcpu_enter_adjust_traps to >>> >>> if ( unlikely(0 != v->domain->arch.monitor.write_ctrlreg_enabled) ) >>> { >>> if ( likely(v->domain->arch.hcr & HCR_TVM) ) >>> return; >>> v->domain->arch.hcr |= HCR_TVM; >>> } >>> else >>> { >>> if ( likely(!(v->domain->arch.hcr & HCR_TVM)) ) >>> return; >>> v->domain->arch.hcr &= ~HCR_TVM; >>> } > > This does not need to be done in vcpu_enter_adjust_traps everytime. > You can set the bit in arch.hcr in DOMCTL_MONITOR_EVENT_WRITE_CTRLREG. I wanted to keep X86-ARM symmetry and it seemed more intuitive to have these kind of adjustments with the vcpu_enter code motion. But now that I think about it, given the fact that we have the guarantee that after monitor_domctl and before reentering the vCPU p2m_restore_state gets called (due to domain_pause/domain_unpause) - thus actually committing the hcr update at the proper time - technically monitor_domctl _is_ the optimal place to set arch.hcr in. In conclusion, I'm thinking of discarding the entire idea of introducing vm_event_vcpu_enter, it seems to me now that this would also render a simpler code. > >>> >>> update_hcr(v->domain); >>> >>> That way at least it's easier to follow where update_hcr is called. > > I don't see much reason to store the value in the domain and have > multiple update_hcr. If we store the value, then we should only call > update_hcr once when returning to the guest. Yep, that will happen with the above-mentioned discarding of vm_event_vcpu_enter idea. > >> And also set the initial value of HCR at the moment of creation, i.e. in >> arch_domain_create as >> >> d->arch.hcr = READ_SYSREG(HCR_EL2) > > We control the value of HCR_EL2, so it would be better to assign the > list of flags here. Right, that will happen too. > > Regards, > Thanks for the useful insights, Corneliu. _______________________________________________ Xen-devel mailing list Xen-devel@lists.xen.org http://lists.xen.org/xen-devel
next prev parent reply other threads:[~2016-06-24 9:32 UTC|newest] Thread overview: 73+ messages / expand[flat|nested] mbox.gz Atom feed top 2016-06-16 14:04 [PATCH 0/7] vm-event: Implement ARM support for control-register writes Corneliu ZUZU 2016-06-16 14:06 ` [PATCH 1/7] minor (formatting) fixes Corneliu ZUZU 2016-06-16 14:24 ` Jan Beulich 2016-06-16 19:19 ` Corneliu ZUZU 2016-06-17 7:06 ` Jan Beulich 2016-06-17 10:46 ` Corneliu ZUZU 2016-06-16 16:02 ` Tamas K Lengyel 2016-06-17 8:33 ` Corneliu ZUZU 2016-06-17 8:36 ` Razvan Cojocaru 2016-06-17 9:29 ` Andrew Cooper 2016-06-17 9:35 ` Jan Beulich 2016-06-17 9:33 ` Jan Beulich 2016-06-17 9:36 ` Razvan Cojocaru 2016-06-17 9:40 ` Jan Beulich 2016-06-17 9:42 ` Razvan Cojocaru 2016-06-17 19:05 ` Tamas K Lengyel 2016-06-16 14:07 ` [PATCH 2/7] vm-event: VM_EVENT_FLAG_DENY requires VM_EVENT_FLAG_VCPU_PAUSED Corneliu ZUZU 2016-06-16 16:11 ` Tamas K Lengyel 2016-06-17 8:43 ` Corneliu ZUZU 2016-06-21 11:26 ` Corneliu ZUZU 2016-06-21 15:09 ` Tamas K Lengyel 2016-06-22 8:34 ` Corneliu ZUZU 2016-06-16 14:08 ` [PATCH 3/7] vm-event: introduce vm_event_vcpu_enter Corneliu ZUZU 2016-06-16 14:51 ` Jan Beulich 2016-06-16 20:10 ` Corneliu ZUZU 2016-06-16 20:33 ` Razvan Cojocaru 2016-06-17 10:41 ` Corneliu ZUZU 2016-06-17 7:17 ` Jan Beulich 2016-06-17 11:13 ` Corneliu ZUZU 2016-06-17 11:27 ` Jan Beulich 2016-06-17 12:13 ` Corneliu ZUZU 2016-06-16 16:17 ` Tamas K Lengyel 2016-06-17 9:19 ` Corneliu ZUZU 2016-06-17 8:55 ` Julien Grall 2016-06-17 11:40 ` Corneliu ZUZU 2016-06-17 13:22 ` Julien Grall 2016-06-16 14:09 ` [PATCH 4/7] vm-event/x86: use vm_event_vcpu_enter properly Corneliu ZUZU 2016-06-16 15:00 ` Jan Beulich 2016-06-16 20:20 ` Corneliu ZUZU 2016-06-17 7:20 ` Jan Beulich 2016-06-17 11:23 ` Corneliu ZUZU 2016-06-16 16:27 ` Tamas K Lengyel 2016-06-17 9:24 ` Corneliu ZUZU 2016-06-16 14:10 ` [PATCH 5/7] x86: replace monitor_write_data.do_write with enum Corneliu ZUZU 2016-06-16 14:12 ` [PATCH 6/7] vm-event/arm: move hvm_event_cr->common vm_event_monitor_cr Corneliu ZUZU 2016-06-16 15:16 ` Jan Beulich 2016-06-17 8:25 ` Corneliu ZUZU 2016-06-17 8:38 ` Jan Beulich 2016-06-17 11:31 ` Corneliu ZUZU 2016-06-21 7:08 ` Corneliu ZUZU 2016-06-21 7:20 ` Jan Beulich 2016-06-21 15:22 ` Tamas K Lengyel 2016-06-22 6:33 ` Jan Beulich 2016-06-16 16:55 ` Tamas K Lengyel 2016-06-17 10:37 ` Corneliu ZUZU 2016-06-16 14:13 ` [PATCH 7/7] vm-event/arm: implement support for control-register write vm-events Corneliu ZUZU 2016-06-16 14:26 ` Julien Grall 2016-06-16 19:24 ` Corneliu ZUZU 2016-06-16 21:28 ` Julien Grall 2016-06-17 11:46 ` Corneliu ZUZU 2016-06-16 16:49 ` Julien Grall 2016-06-17 10:36 ` Corneliu ZUZU 2016-06-17 13:18 ` Julien Grall 2016-06-22 16:35 ` Corneliu ZUZU 2016-06-22 17:17 ` Julien Grall 2016-06-22 18:39 ` Corneliu ZUZU 2016-06-22 19:37 ` Corneliu ZUZU 2016-06-22 19:41 ` Julien Grall 2016-06-23 5:31 ` Corneliu ZUZU 2016-06-23 5:49 ` Corneliu ZUZU 2016-06-23 11:11 ` Julien Grall 2016-06-24 9:32 ` Corneliu ZUZU [this message] 2016-06-23 11:00 ` Julien Grall
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