linux-kernel - Re: About add an A64FX cache control function into resctrl

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Date:   Fri, 30 Apr 2021 12:46:32 +0100
From:   Catalin Marinas <catalin.marinas@....com>
To:     "Luck, Tony" <tony.luck@...el.com>
Cc:     "Chatre, Reinette" <reinette.chatre@...el.com>,
        "tan.shaopeng@...itsu.com" <tan.shaopeng@...itsu.com>,
        "Yu, Fenghua" <fenghua.yu@...el.com>,
        "'linux-kernel@...r.kernel.org'" <linux-kernel@...r.kernel.org>,
        "'linux-arm-kernel@...ts.infradead.org'" 
        <linux-arm-kernel@...ts.infradead.org>,
        'James Morse' <james.morse@....com>,
        "misono.tomohiro@...itsu.com" <misono.tomohiro@...itsu.com>
Subject: Re: About add an A64FX cache control function into resctrl

On Thu, Apr 29, 2021 at 05:50:20PM +0000, Luck, Tony wrote:
> >>>> [Sector cache function]
> >>>> The sector cache function split cache into multiple sectors and
> >>>> control them separately. It is implemented on the L1D cache and
> >>>> L2 cache in the A64FX processor and can be controlled individually
> >>>> for L1D cache and L2 cache. A64FX has no L3 cache. Each L1D cache and
> >>>> L2 cache has 4 sectors. Which L1D sector is used is specified by the
> >>>> value of [57:56] bits of address, how many ways of sector are
> >>>> specified by the value of register (IMP_SCCR_L1_EL0).
> >>>> Which L2 sector is used is specified by the value of [56] bits of
> >>>> address, and how many ways of sector are specified by value of
> >>>> register (IMP_SCCR_ASSIGN_EL1, IMP_SCCR_SET0_L2_EL1,
> >>>> IMP_SCCR_SET1_L2_EL1).
> 
> Are A64FX binaries position independent?  I.e. could the OS reassign
> a running task to a different sector by remapping it to different virtual
> addresses during a context switch?

Arm64 supports a maximum of 52-bit of virtual or physical addresses. The
maximum the MMU would produce would be a 52-bit output address. I
presume bits 56, 57 of the address bus are used for some cache affinity
(sector selection) but they don't influence the memory addressing, nor
could the MMU set them.

-- 
Catalin