linux-kernel - Re: [PATCH 6/7] acpi, apei, ghes: Make unmapping functionality independent from architecture.

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Date:	Wed, 14 May 2014 13:35:42 +0100
From:	Will Deacon <will.deacon@....com>
To:	Tomasz Nowicki <tomasz.nowicki@...aro.org>
Cc:	Borislav Petkov <bp@...en8.de>,
	Catalin Marinas <Catalin.Marinas@....com>,
	Russell King - ARM Linux <linux@....linux.org.uk>,
	"rjw@...ysocki.net" <rjw@...ysocki.net>,
	"lenb@...nel.org" <lenb@...nel.org>,
	"tony.luck@...el.com" <tony.luck@...el.com>,
	"bp@...e.de" <bp@...e.de>,
	"m.chehab@...sung.com" <m.chehab@...sung.com>,
	"linux-edac@...r.kernel.org" <linux-edac@...r.kernel.org>,
	"x86@...nel.org" <x86@...nel.org>,
	"linux-acpi@...r.kernel.org" <linux-acpi@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linaro-acpi@...ts.linaro.org" <linaro-acpi@...ts.linaro.org>
Subject: Re: [PATCH 6/7] acpi, apei, ghes: Make unmapping functionality
 independent from architecture.

On Wed, May 14, 2014 at 01:32:27PM +0100, Tomasz Nowicki wrote:
> On 13.05.2014 22:11, Borislav Petkov wrote:
> > On Wed, Apr 09, 2014 at 05:14:34PM +0200, Tomasz Nowicki wrote:
> >> Till now __flush_tlb_one was used for unmapping virtual memory which
> >> is x86 specific function. Replace it with more generic
> >> flush_tlb_kernel_range.
> >>
> >> Signed-off-by: Tomasz Nowicki <tomasz.nowicki@...aro.org>
> >> ---
> >>   drivers/acpi/apei/ghes.c |    4 ++--
> >>   1 file changed, 2 insertions(+), 2 deletions(-)
> >>
> >> diff --git a/drivers/acpi/apei/ghes.c b/drivers/acpi/apei/ghes.c
> >> index aaf8db3..624878b 100644
> >> --- a/drivers/acpi/apei/ghes.c
> >> +++ b/drivers/acpi/apei/ghes.c
> >> @@ -185,7 +185,7 @@ static void ghes_iounmap_nmi(void __iomem *vaddr_ptr)
> >>
> >>   	BUG_ON(vaddr != (unsigned long)GHES_IOREMAP_NMI_PAGE(base));
> >>   	unmap_kernel_range_noflush(vaddr, PAGE_SIZE);
> >> -	__flush_tlb_one(vaddr);
> >> +	flush_tlb_kernel_range(vaddr, vaddr + PAGE_SIZE);
> >>   }
> >>
> >>   static void ghes_iounmap_irq(void __iomem *vaddr_ptr)
> >> @@ -195,7 +195,7 @@ static void ghes_iounmap_irq(void __iomem *vaddr_ptr)
> >>
> >>   	BUG_ON(vaddr != (unsigned long)GHES_IOREMAP_IRQ_PAGE(base));
> >>   	unmap_kernel_range_noflush(vaddr, PAGE_SIZE);
> >> -	__flush_tlb_one(vaddr);
> >> +	flush_tlb_kernel_range(vaddr, vaddr + PAGE_SIZE);
> >
> > flush_tlb_kernel_range() does send an IPI to every core on x86 which is
> > much more expensive than what __flush_tlb_one does.
> >
> > Fairer it would be if you added a __flush_tlb_one() version for arm
> > which does flush_tlb_kernel_range for you.
> >
> 
> Thanks for comment. I am not sure if maintainers will allow me to add 
> sth like __flush_tlb_one() for arm/arm64. Let me ask them directly. 
> Catalin, Russell what do you think?

I don't have the background for this, but if you don't need broadcasting
(if this avoids IPIs on x86, I guess you don't) then why not use
local_flush_tlb_kernel_range instead?

Will
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