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

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Message-ID: <20140514124834.GH10145@arm.com>
Date:	Wed, 14 May 2014 13:48:34 +0100
From:	Will Deacon <will.deacon@....com>
To:	Catalin Marinas <catalin.marinas@....com>
Cc:	Tomasz Nowicki <tomasz.nowicki@...aro.org>,
	Borislav Petkov <bp@...en8.de>,
	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 01:45:07PM +0100, Catalin Marinas wrote:
> On Wed, May 14, 2014 at 01:35:42PM +0100, Will Deacon wrote:
> > 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?
> 
> Is this generic enough (we don't have it on arm64)?

Well, it's more popular than __flush_tlb_one and the naming is more
descriptive imo.

Will
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