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Re: [PATCH v3 08/18] xen/arm32: head: Introduce an helper to flush the TLBs
On 14/12/2022 14:24, Michal Orzel wrote:
Hi Julien,
Hi Michal,
On 12/12/2022 10:55, Julien Grall wrote:
From: Julien Grall <jgrall@xxxxxxxxxx>
The sequence for flushing the TLBs is 4 instruction long and often
requires an explanation how it works.
So create an helper and use it in the boot code (switch_ttbr() is left
Here and in title: s/an helper/a helper/
Done.
alone for now).
Could you explain why?
So we need to decide how we expect switch_ttbr(). E.g. if Xen is
relocated at a different, should the caller take care of the
instruction/branch predictor flush?
I have expanded to "switch_ttbr() is left alone until we decided the
semantic of the call".
Note that in secondary_switched, we were also flushing the instruction
cache and branch predictor. Neither of them was necessary because:
* We are only supporting IVIPT cache on arm32, so the instruction
cache flush is only necessary when executable code is modified.
None of the boot code is doing that.
* The instruction cache is not invalidated and misprediction is not
a problem at boot.
Signed-off-by: Julien Grall <jgrall@xxxxxxxxxx>
Apart from that, the patch is good, so:
Reviewed-by: Michal Orzel <michal.orzel@xxxxxxx>
Thanks!
---
Changes in v3:
* Fix typo
* Update the documentation
* Rename the argument from tmp1 to tmp
---
xen/arch/arm/arm32/head.S | 30 +++++++++++++++++-------------
1 file changed, 17 insertions(+), 13 deletions(-)
diff --git a/xen/arch/arm/arm32/head.S b/xen/arch/arm/arm32/head.S
index 40c1d7502007..315abbbaebec 100644
--- a/xen/arch/arm/arm32/head.S
+++ b/xen/arch/arm/arm32/head.S
@@ -66,6 +66,20 @@
add \rb, \rb, r10
.endm
+/*
+ * Flush local TLBs
+ *
+ * @tmp: Scratch register
As you are respinning a series anyway, could you add just one space after @tmp:?
Ok.
Cheers,
--
Julien Grall
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