From: Julien Grall <julien.grall@linaro.org>
To: Ian Campbell <Ian.Campbell@citrix.com>
Cc: stefano.stabellini@eu.citrix.com, tim@xen.org, xen-devel@lists.xen.org
Subject: Re: [PATCH 4/9] xen: arm: turn vtimer traps for cp32/64 and sysreg into #undef
Date: Wed, 10 Sep 2014 11:54:32 -0700 [thread overview]
Message-ID: <54109E68.7020102@linaro.org> (raw)
In-Reply-To: <1410342387.8217.272.camel@kazak.uk.xensource.com>
Hi Ian,
On 10/09/14 02:46, Ian Campbell wrote:
> On Tue, 2014-09-09 at 16:31 -0700, Julien Grall wrote:
>> Hi Ian,
>>
>> On 09/09/14 09:23, Ian Campbell wrote:
>>> We have allowed EL1 to access these registers directly for some time
>>> (at least since 4.3.0). They were only ever trapped to support very
>>> early models which had a buggy hypervisor timer, requiring us to use
>>> the phys timer for Xen itself.
>>> In the interests of minimising the patch for the security update just
>>> remove the call to vtimer_emulate and inject an #undef exception. In
>>> practice we will never see any of these traps.
>>
>> I disagree with the commit message, a guest may use the physical timer
>> rather than the virtual timer. It's the case when a guest doesn't have
>> the necessary code to use the virtual timer.
>
> I think you've misunderstood. The guest is allowed direct access to the
> physical timer ever since we removed the workaround for the buggy
> hypervisor timer on the models. Hence we are never trapping these
> registers anyway. Probably I should go further here and actually remove
> all the phys timer emulation support from vtimer.c.
Are you sure? In init_interrupt_timer (xen/arch/arm/timer.c) we disable
the access to the physical timer to the guest. See
WRITE_SYSREG32(CNTHCTL_PA, CNTHCTL_EL2).
Hence, I don't see any save/restore for the physical timer in
xen/arch/arm/vtimer.c. I only see them for the virtual timer.
Regards,
--
Julien Grall
next prev parent reply other threads:[~2014-09-10 18:54 UTC|newest]
Thread overview: 31+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-09-09 16:22 [RFC PATCH 0/9] xen: arm: reenable support for 32-bit userspace running in 64-bit guest Ian Campbell
2014-09-09 16:23 ` [PATCH 1/9] xen: arm: Correct PMXEV cp register definitions Ian Campbell
2014-09-09 23:04 ` Julien Grall
2014-09-09 16:23 ` [PATCH 2/9] xen: arm: Factor out psr_mode_is_user Ian Campbell
2014-09-09 23:08 ` Julien Grall
2014-09-09 16:23 ` [PATCH 3/9] xen: arm: Handle 32-bit EL0 on 64-bit EL1 when advancing PC after trap Ian Campbell
2014-09-09 23:12 ` Julien Grall
2014-09-09 16:23 ` [PATCH 4/9] xen: arm: turn vtimer traps for cp32/64 and sysreg into #undef Ian Campbell
2014-09-09 23:31 ` Julien Grall
2014-09-10 9:46 ` Ian Campbell
2014-09-10 18:54 ` Julien Grall [this message]
2014-09-11 8:43 ` Ian Campbell
2015-01-14 16:33 ` Ian Campbell
2015-01-14 16:57 ` Julien Grall
2015-01-15 10:26 ` Ian Campbell
2015-01-15 12:27 ` Julien Grall
2015-01-15 12:35 ` Ian Campbell
2014-09-09 16:23 ` [PATCH 5/9] xen: arm: Handle CP15 register traps from userspace Ian Campbell
2014-09-09 23:42 ` Julien Grall
2014-09-10 9:48 ` Ian Campbell
2014-09-10 18:56 ` Julien Grall
2014-09-18 1:31 ` Ian Campbell
2014-09-09 16:23 ` [PATCH 6/9] xen: arm: Handle CP14 32-bit register accesses " Ian Campbell
2014-09-09 23:45 ` Julien Grall
2014-09-10 9:48 ` Ian Campbell
2015-02-10 3:40 ` Ian Campbell
2015-02-10 4:14 ` Julien Grall
2014-09-09 16:23 ` [PATCH 7/9] xen: arm: correctly handle sysreg " Ian Campbell
2014-09-09 16:23 ` [PATCH 8/9] xen: arm: handle remaining traps " Ian Campbell
2014-09-09 16:23 ` [PATCH 9/9] xen: arm: Allow traps from 32 bit userspace on 64 bit hypervisors again Ian Campbell
2014-09-09 16:23 ` [RFC PATCH 0/9] xen: arm: reenable support for 32-bit userspace running in 64-bit guest Ian Campbell
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