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From: Julien Grall <julien.grall@arm.com>
To: Corneliu ZUZU <czuzu@bitdefender.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: Thu, 23 Jun 2016 12:00:14 +0100	[thread overview]
Message-ID: <576BC13E.5030902@arm.com> (raw)
In-Reply-To: <576AC834.2010701@arm.com>

Hello,

On 22/06/16 18:17, Julien Grall wrote:
> On 22/06/16 17:35, Corneliu ZUZU wrote:
>
>> Julien,
>
> Hello Corneliu,
>
>> 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.
>
> After the first write to HCR_EL2, "hcr" still have the VM bit set as we
> only mask it. So the second write will re-set the VM bit.
>
> I am not sure why the VM bit is unset/set in this function. I am not
> able to find a paragraph justifying it in the ARM ARM. I have CCed some
> ARM folks to check if I missed something.

After talking with different ARM folks, I confirm that it is not 
necessary to disable the HCR_VM before setting TTBR0.

Regards,

-- 
Julien Grall

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

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