From mboxrd@z Thu Jan  1 00:00:00 1970
From: marc.zyngier@arm.com (Marc Zyngier)
Date: Wed, 21 Feb 2018 17:52:41 +0000
Subject: [PATCH v4 10/40] KVM: arm64: Slightly improve debug save/restore
 functions
In-Reply-To: <20180221173903.xlpwnlrnjlpatm5s@kamzik.brq.redhat.com>
References: <20180215210332.8648-1-christoffer.dall@linaro.org>
 <20180215210332.8648-11-christoffer.dall@linaro.org>
 <20180221173903.xlpwnlrnjlpatm5s@kamzik.brq.redhat.com>
Message-ID: <37712e4f-7f47-2101-71f5-d024a7993f13@arm.com>
To: linux-arm-kernel@lists.infradead.org
List-Id: linux-arm-kernel.lists.infradead.org

On 21/02/18 17:39, Andrew Jones wrote:
> On Thu, Feb 15, 2018 at 10:03:02PM +0100, Christoffer Dall wrote:
>> The debug save/restore functions can be improved by using the has_vhe()
>> static key instead of the instruction alternative.  Using the static key
>> uses the same paradigm as we're going to use elsewhere, it makes the
>> code more readable, and it generates slightly better code (no
>> stack setups and function calls unless necessary).
>>
>> We also use a static key on the restore path, because it will be
>> marginally faster than loading a value from memory.
>>
>> Finally, we don't have to conditionally clear the debug dirty flag if
>> it's set, we can just clear it.
>>
>> Reviewed-by: Marc Zyngier <marc.zyngier@arm.com>
>> Signed-off-by: Christoffer Dall <christoffer.dall@linaro.org>
>> ---
>>
>> Notes:
>>     Changes since v1:
>>      - Change dot to comma in comment
>>      - Rename __debug_restore_spe to __debug_restore_spe_nvhe
>>
>>  arch/arm64/kvm/hyp/debug-sr.c | 26 ++++++++++++--------------
>>  1 file changed, 12 insertions(+), 14 deletions(-)
>>
> 
> Maybe after this series is merged, if there are any hyp_alternate_select's
> left, we can replace all the remaining ones with has_vhe() and then just
> completely remove hyp_alternate_select.

Note that older compilers (such as GCC 4.8) will generate horrible code
with static keys, as they do not support "asm goto". Not that I want to
preserve the home brew hyp_alternate_select mechanism, but I just want
to make it plain that some distros will definitely suffer from the
transition.

	M.
-- 
Jazz is not dead. It just smells funny...