linux-kernel - Re: [PATCH v4 1/3] arm64: Improve kernel address detection of __is_lm

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Message-ID: <20210125173829.GB4565@C02TD0UTHF1T.local>
Date:   Mon, 25 Jan 2021 17:38:29 +0000
From:   Mark Rutland <mark.rutland@....com>
To:     Catalin Marinas <catalin.marinas@....com>
Cc:     Vincenzo Frascino <vincenzo.frascino@....com>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        kasan-dev@...glegroups.com,
        Andrey Ryabinin <aryabinin@...tuozzo.com>,
        Alexander Potapenko <glider@...gle.com>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Leon Romanovsky <leonro@...lanox.com>,
        Andrey Konovalov <andreyknvl@...gle.com>,
        Will Deacon <will@...nel.org>,
        "Paul E . McKenney" <paulmck@...nel.org>,
        Naresh Kamboju <naresh.kamboju@...aro.org>
Subject: Re: [PATCH v4 1/3] arm64: Improve kernel address detection of
 __is_lm_address()

On Mon, Jan 25, 2021 at 02:59:12PM +0000, Catalin Marinas wrote:
> On Mon, Jan 25, 2021 at 02:36:34PM +0000, Vincenzo Frascino wrote:
> > On 1/25/21 1:02 PM, Mark Rutland wrote:
> > > On Fri, Jan 22, 2021 at 03:56:40PM +0000, Vincenzo Frascino wrote:
> > > This patch itself looks fine, but it's not going to backport very far,
> > > so I suspect we might need to write a preparatory patch that adds an
> > > explicit range check to virt_addr_valid() which can be trivially
> > > backported.
> > 
> > I checked the old releases and I agree this is not back-portable as it stands.
> > I propose therefore to add a preparatory patch with the check below:
> > 
> > #define __is_ttrb1_address(addr)	((u64)(addr) >= PAGE_OFFSET && \
> > 
> > If it works for you I am happy to take care of it and post a new version of my
> > patches.
> 
> I'm not entirely sure we need a preparatory patch. IIUC (it needs
> checking), virt_addr_valid() was fine until 5.4, broken by commit
> 14c127c957c1 ("arm64: mm: Flip kernel VA space").

Ah, so it was; thanks for digging into the history!

> Will addressed the
> flip case in 68dd8ef32162 ("arm64: memory: Fix virt_addr_valid() using
> __is_lm_address()") but this broke the <PAGE_OFFSET case. So in 5.4 a
> NULL address is considered valid.
> 
> Ard's commit f4693c2716b3 ("arm64: mm: extend linear region for 52-bit
> VA configurations") changed the test to no longer rely on va_bits but
> did not change the broken semantics.
> 
> If Ard's change plus the fix proposed in this test works on 5.4, I'd say
> we just merge this patch with the corresponding Cc stable and Fixes tags
> and tweak it slightly when doing the backports as it wouldn't apply
> cleanly. IOW, I wouldn't add another check to virt_addr_valid() as we
> did not need one prior to 5.4.

That makes sense to me; sorry for the noise!

Thanks,
Mark.