From: Marc Zyngier <maz@kernel.org>
To: Pavel Tatashin <pasha.tatashin@soleen.com>
Cc: James Morris <jmorris@namei.org>, Sasha Levin <sashal@kernel.org>,
"Eric W. Biederman" <ebiederm@xmission.com>,
kexec mailing list <kexec@lists.infradead.org>,
LKML <linux-kernel@vger.kernel.org>,
Jonathan Corbet <corbet@lwn.net>,
Catalin Marinas <catalin.marinas@arm.com>,
Will Deacon <will@kernel.org>,
Linux ARM <linux-arm-kernel@lists.infradead.org>,
James Morse <james.morse@arm.com>,
Vladimir Murzin <vladimir.murzin@arm.com>,
Matthias Brugger <matthias.bgg@gmail.com>,
linux-mm <linux-mm@kvack.org>,
Mark Rutland <mark.rutland@arm.com>,
steve.capper@arm.com, rfontana@redhat.com,
Thomas Gleixner <tglx@linutronix.de>,
Selin Dag <selindag@gmail.com>,
Tyler Hicks <tyhicks@linux.microsoft.com>,
Pingfan Liu <kernelfans@gmail.com>,
Andrew Morton <akpm@linux-foundation.org>,
madvenka@linux.microsoft.com
Subject: Re: [PATCH 03/18] arm64: hyp-stub: Move elx_sync into the vectors
Date: Tue, 01 Jun 2021 13:22:57 +0100 [thread overview]
Message-ID: <87r1hl22qm.wl-maz@kernel.org> (raw)
In-Reply-To: <CA+CK2bDvsFX_s-G5tRcE1GreNW_xLTognosUFbPPgaUK7-cafQ@mail.gmail.com>
On Thu, 27 May 2021 22:23:22 +0100,
Pavel Tatashin <pasha.tatashin@soleen.com> wrote:
>
> On Thu, May 27, 2021 at 11:54 AM Marc Zyngier <maz@kernel.org> wrote:
> >
> > On Thu, 27 May 2021 16:05:11 +0100,
> > Pavel Tatashin <pasha.tatashin@soleen.com> wrote:
> > >
> > > The hyp-stub's elx_sync code fits in the vector.
> > >
> > > With this, all of the hyp-stubs behaviour is contained in its vectors.
> > > This lets kexec and hibernate copy the hyp-stub when they need its
> > > behaviour, instead of re-implementing it.
> > >
> > > Co-developed-by: James Morse <james.morse@arm.com>
> > > Signed-off-by: Pavel Tatashin <pasha.tatashin@soleen.com>
> > > ---
> > > arch/arm64/kernel/hyp-stub.S | 64 +++++++++++++++++++-----------------
> > > 1 file changed, 33 insertions(+), 31 deletions(-)
> > >
> > > diff --git a/arch/arm64/kernel/hyp-stub.S b/arch/arm64/kernel/hyp-stub.S
> > > index 18a97bee3779..86af6c4e52b9 100644
> > > --- a/arch/arm64/kernel/hyp-stub.S
> > > +++ b/arch/arm64/kernel/hyp-stub.S
> > > @@ -21,6 +21,37 @@ SYM_CODE_START_LOCAL(\label)
> > > .align 7
> > > b \label
> > > SYM_CODE_END(\label)
> > > +.endm
> > > +
> > > +.macro elx_sync_vector label
> > > +SYM_CODE_START_LOCAL(\label)
> > > + .align 7
> > > + cmp x0, #HVC_SET_VECTORS
> > > + b.ne 1f
> > > + msr vbar_el2, x1
> > > + b 9f
> > > +
> > > +1: cmp x0, #HVC_VHE_RESTART
> > > + b.eq mutate_to_vhe
> >
> > Now that this has turned into a macro, what are the guarantees that
> > mutate_to_vhe will be within reach of the site where this macro is
> > expanded? It does work here, but what about the other expansion sites
> > that will show up later in the series?
> >
> > What was wrong with directly branching to the original call site?
> > Nothing in the commit message explains it.
>
> Hi Marc,
>
> I need to explain this better in the commit log. Later in the series
> we create our own vector copy that is outside of the old and new
> kernel so it does not get overwritten during kexec relocation. When
> VHE is enabled, the vector is passed so we can switch to el2 before
> jumping to the new kernel.
>
> arm64_relocate_new_kernel() which performs the relocation runs with
> MMU being enabled until relocation is done, after that disables MMU
> and if vectors are passed performs:
>
> mov x0, #HVC_SOFT_RESTART
> hvc #0 /* Jumps from el2 */
>
> It cannot call mutate_to_vhe because #HVC_VHE_RESTART is not used
> here. But, if it had to it would not work as we cannot return to the
> old kernel text after relocation.
OK, so you are happy with having a dangling branch pointing to
nowhere? Something in me screams that it isn't a good idea, in
general.
If HVC_SOFT_RESTART is all you need, I'd rather you have a small stub
that implements exactly that and nothing else. Feel free to extract it
as a reusable macro if you want.
Thanks,
M.
--
Without deviation from the norm, progress is not possible.
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next prev parent reply other threads:[~2021-06-01 12:24 UTC|newest]
Thread overview: 27+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-05-27 15:05 [PATCH 00/18] arm64: MMU enabled kexec relocation Pavel Tatashin
2021-05-27 15:05 ` [PATCH 01/18] arm64: hyp-stub: Check the size of the HYP stub's vectors Pavel Tatashin
2021-05-27 15:05 ` [PATCH 02/18] arm64: hyp-stub: Move invalid vector entries into the vectors Pavel Tatashin
2021-05-27 15:05 ` [PATCH 03/18] arm64: hyp-stub: Move elx_sync " Pavel Tatashin
2021-05-27 15:54 ` Marc Zyngier
2021-05-27 21:23 ` Pavel Tatashin
2021-06-01 12:22 ` Marc Zyngier [this message]
2021-06-02 1:18 ` Pavel Tatashin
2021-06-08 17:46 ` Pavel Tatashin
2021-05-27 15:05 ` [PATCH 04/18] arm64: kernel: add helper for booted at EL2 and not VHE Pavel Tatashin
2021-06-01 12:38 ` Marc Zyngier
2021-06-02 1:33 ` Pavel Tatashin
2021-06-02 8:20 ` Marc Zyngier
2021-05-27 15:05 ` [PATCH 05/18] arm64: trans_pgd: hibernate: Add trans_pgd_copy_el2_vectors Pavel Tatashin
2021-05-27 15:05 ` [PATCH 06/18] arm64: hibernate: abstract ttrb0 setup function Pavel Tatashin
2021-05-27 15:05 ` [PATCH 07/18] arm64: kexec: flush image and lists during kexec load time Pavel Tatashin
2021-05-27 15:05 ` [PATCH 08/18] arm64: kexec: skip relocation code for inplace kexec Pavel Tatashin
2021-05-27 15:05 ` [PATCH 09/18] arm64: kexec: Use dcache ops macros instead of open-coding Pavel Tatashin
2021-05-27 15:05 ` [PATCH 10/18] arm64: kexec: pass kimage as the only argument to relocation function Pavel Tatashin
2021-05-27 15:05 ` [PATCH 11/18] arm64: kexec: kexec may require EL2 vectors Pavel Tatashin
2021-05-27 15:05 ` [PATCH 12/18] arm64: kexec: relocate in EL1 mode Pavel Tatashin
2021-05-27 15:05 ` [PATCH 13/18] arm64: kexec: use ld script for relocation function Pavel Tatashin
2021-05-27 15:05 ` [PATCH 14/18] arm64: kexec: install a copy of the linear-map Pavel Tatashin
2021-05-27 15:05 ` [PATCH 15/18] arm64: kexec: keep MMU enabled during kexec relocation Pavel Tatashin
2021-05-27 15:05 ` [PATCH 16/18] arm64: kexec: remove the pre-kexec PoC maintenance Pavel Tatashin
2021-05-27 15:05 ` [PATCH 17/18] arm64: kexec: Remove cpu-reset.h Pavel Tatashin
2021-05-27 15:05 ` [PATCH 18/18] arm64/mm: remove useless trans_pgd_map_page() Pavel Tatashin
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