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From: Corneliu ZUZU <czuzu@bitdefender.com>
To: Julien Grall <julien.grall@arm.com>, xen-devel@lists.xen.org
Cc: Stefano Stabellini <sstabellini@kernel.org>,
	Tamas K Lengyel <tamas@tklengyel.com>,
	Razvan Cojocaru <rcojocaru@bitdefender.com>
Subject: Re: [PATCH 7/7] vm-event/arm: implement support for control-register write vm-events
Date: Wed, 22 Jun 2016 19:35:06 +0300	[thread overview]
Message-ID: <bfcf0866-134e-ab41-8c5f-498dc685bb08@bitdefender.com> (raw)
In-Reply-To: <196523e7-285c-51a3-c48a-eff45d40a342@bitdefender.com>

On 6/17/2016 1:36 PM, Corneliu ZUZU wrote:
> On 6/16/2016 7:49 PM, Julien Grall wrote:
>> Hello Corneliu,
>>
>> On 16/06/16 15:13, Corneliu ZUZU wrote:
>>
>>> +    case MWS_TTBCR:
>>> +        MWS_EMUL(TTBCR);
>>> +        break;
>>> +    default:
>>> +        break;
>>> +    }
>>> +
>>> +    w->status = MWS_NOWRITE;
>>> +}
>>> +
>>> +static inline void vcpu_enter_adjust_traps(struct vcpu *v)
>>> +{
>>> +    register_t old_hcr, hcr;
>>> +
>>> +    hcr = (old_hcr = READ_SYSREG(HCR_EL2));
>>> +
>>> +    if ( unlikely(0 != 
>>> v->domain->arch.monitor.write_ctrlreg_enabled) )
>>> +        hcr |= HCR_TVM;
>>> +    else
>>> +        hcr &= ~HCR_TVM;
>>> +
>>> +    if ( unlikely(hcr != old_hcr) )
>>> +    {
>>> +        WRITE_SYSREG(hcr, HCR_EL2);
>>> +        isb();
>>> +    }
>>
>> The HCR register is also updated in p2m_restore_state to set 
>> HCR_EL2.RW. I would prefer to have a single place where HCR is updated.
>>
>> Maybe we should store the HCR value per-domain?
>
> Yes, that would be nice. Will look into that for v2.

Julien,

I was trying to implement having HCR stored in arch_domain or arch_vcpu 
as suggested above and I'm a bit confused about the code in 
p2m_restore_state.
I'm hoping you can provide some feedback on this matter. Here's the 
current implementation of the function:

     void p2m_restore_state(struct vcpu *n)
     {
         register_t hcr;

         hcr = READ_SYSREG(HCR_EL2);
         WRITE_SYSREG(hcr & ~HCR_VM, HCR_EL2);
         isb();

         p2m_load_VTTBR(n->domain);
         isb();

         if ( is_32bit_domain(n->domain) )
             hcr &= ~HCR_RW;
         else
             hcr |= HCR_RW;

         WRITE_SYSREG(n->arch.sctlr, SCTLR_EL1);
         isb();

         WRITE_SYSREG(hcr, HCR_EL2);
         isb();
     }

First of all, I see the HCR_VM bit being unset (=0) but I don't quite 
understand why and even more peculiar is the fact that I couldn't find 
any place where the bit is set (=1) again.
Secondly, why this order of operations? More specifically, why is 
p2m_load_VTTBR done after the HCR_VM bit is unset and before the HCR_RW 
bit is set/unset? Can't we write HCR only once here?
And finally, I see the function is called by construct_dom0. The code 
there looks like:

     /*
      * The following loads use the domain's p2m and require current to
      * be a vcpu of the domain, temporarily switch
      */
     saved_current = current;
     p2m_restore_state(v);
     [...]
     /* Now that we are done restore the original p2m and current. */
     set_current(saved_current);
     p2m_restore_state(saved_current);

I suppose the significant changes p2m_restore_state does for the code in 
between ("[...]") is setting VTTBR & SCTLR which are used by translation 
functions such as gvirt_to_maddr (which seems to use PAR_EL1).
What I don't grasp is what effect setting the VTTBR has if HCR.HCR_VM is 
unset and left unset...

Thanks,
Corneliu.

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  parent reply	other threads:[~2016-06-22 16:35 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 [this message]
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
2016-06-23 11:00           ` Julien Grall

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