RE: [PATCH v4 03/14] xen/arm32: flushtlb: Reduce scope of barrier for local TLB flush

From: Henry Wang <Henry.Wang@arm.com>
To: Julien Grall <julien@xen.org>,
	"xen-devel@lists.xenproject.org" <xen-devel@lists.xenproject.org>
Cc: Luca Fancellu <Luca.Fancellu@arm.com>,
	Julien Grall <jgrall@amazon.com>,
	Stefano Stabellini <sstabellini@kernel.org>,
	Bertrand Marquis <Bertrand.Marquis@arm.com>,
	Volodymyr Babchuk <Volodymyr_Babchuk@epam.com>,
	Michal Orzel <michal.orzel@amd.com>
Subject: RE: [PATCH v4 03/14] xen/arm32: flushtlb: Reduce scope of barrier for local TLB flush
Date: Fri, 13 Jan 2023 13:46:31 +0000	[thread overview]
Message-ID: <AS8PR08MB7991982E6F5F7AA43820997492C29@AS8PR08MB7991.eurprd08.prod.outlook.com> (raw)
In-Reply-To: <20230113101136.479-4-julien@xen.org>

Hi Julien,

> -----Original Message-----
> Subject: [PATCH v4 03/14] xen/arm32: flushtlb: Reduce scope of barrier for
> local TLB flush
> 
> From: Julien Grall <jgrall@amazon.com>
> 
> Per G5-9224 in ARM DDI 0487I.a:
> 
> "A DSB NSH is sufficient to ensure completion of TLB maintenance
>  instructions that apply to a single PE. A DSB ISH is sufficient to
>  ensure completion of TLB maintenance instructions that apply to PEs
>  in the same Inner Shareable domain.
> "
> 
> This is quoting the Armv8 specification because I couldn't find an
> explicit statement in the Armv7 specification. Instead, I could find
> bits in various places that confirm the same implementation.
> 
> Furthermore, Linux has been using 'nsh' since 2013 (62cbbc42e001
> "ARM: tlb: reduce scope of barrier domains for TLB invalidation").
> 
> This means barrier after local TLB flushes could be reduced to
> non-shareable.
> 
> Signed-off-by: Julien Grall <jgrall@amazon.com>
> Reviewed-by: Michal Orzel <michal.orzel@amd.com>

I've tested this patch on FVP in arm32 execution mode using the same
testing approach for patch#1, and this patch is good, so:

Tested-by: Henry Wang <Henry.Wang@arm.com>

Kind regards,
Henry