linux-kernel - Re: [PATCH] powerpc/svm: Don't issue ultracalls if !mem_encrypt

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Date:   Fri, 13 Aug 2021 18:54:34 +0200
From:   Borislav Petkov <bp@...en8.de>
To:     Michael Ellerman <mpe@...erman.id.au>,
        Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
Cc:     Will Deacon <will@...nel.org>, linux-kernel@...r.kernel.org,
        Sachin Sant <sachinp@...ux.vnet.ibm.com>,
        linuxppc-dev@...ts.ozlabs.org, Robin Murphy <robin.murphy@....com>,
        Nicholas Piggin <npiggin@...il.com>,
        Nathan Chancellor <nathan@...nel.org>,
        iommu@...ts.linux-foundation.org,
        Claire Chang <tientzu@...omium.org>,
        Christoph Hellwig <hch@....de>,
        Tom Lendacky <thomas.lendacky@....com>
Subject: Re: [PATCH] powerpc/svm: Don't issue ultracalls if
 !mem_encrypt_active()

On Mon, Aug 02, 2021 at 09:20:30PM +1000, Michael Ellerman wrote:
> Will Deacon <will@...nel.org> writes:
> > Commit ad6c00283163 ("swiotlb: Free tbl memory in swiotlb_exit()")
> > introduced a set_memory_encrypted() call to swiotlb_exit() so that the
> > buffer pages are returned to an encrypted state prior to being freed.
> >
> > Sachin reports that this leads to the following crash on a Power server:
> >
> > [    0.010799] software IO TLB: tearing down default memory pool
> > [    0.010805] ------------[ cut here ]------------
> > [    0.010808] kernel BUG at arch/powerpc/kernel/interrupt.c:98!
> >
> > Nick spotted that this is because set_memory_encrypted() is issuing an
> > ultracall which doesn't exist for the processor, and should therefore
> > be gated by mem_encrypt_active() to mirror the x86 implementation.
> >
> > Cc: Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
> > Cc: Claire Chang <tientzu@...omium.org>
> > Cc: Christoph Hellwig <hch@....de>
> > Cc: Robin Murphy <robin.murphy@....com>
> > Fixes: ad6c00283163 ("swiotlb: Free tbl memory in swiotlb_exit()")
> > Suggested-by: Nicholas Piggin <npiggin@...il.com>
> > Reported-by: Sachin Sant <sachinp@...ux.vnet.ibm.com>
> > Tested-by: Sachin Sant <sachinp@...ux.vnet.ibm.com>
> > Tested-by: Nathan Chancellor <nathan@...nel.org>
> > Link: https://lore.kernel.org/r/1905CD70-7656-42AE-99E2-A31FC3812EAC@linux.vnet.ibm.com/
> > Signed-off-by: Will Deacon <will@...nel.org>
> > ---
> >  arch/powerpc/platforms/pseries/svm.c | 6 ++++++
> >  1 file changed, 6 insertions(+)
> 
> Thanks.
> 
> Acked-by: Michael Ellerman <mpe@...erman.id.au>
> 
> 
> I assume Konrad will take this via the swiotlb tree?

Btw, we're currently reworking that whole "am I running as a
confidential guest" querying, see:

https://lkml.kernel.org/r/029791b24c6412f9427cfe6ec598156c64395964.1627424774.git.thomas.lendacky@amd.com

for example.

I see Konrad has queued this for 5.15 in his devel/for-linus-5.15 branch
so if he sends it to Linus in the upcoming merge window (right Konrad?)
then I can base the rework ontop, once 5.15-rc1 releases, so that there
are no build breakages...

Thx.

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette