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Date: Mon, 02 Aug 2021 12:03:19 +1000
From: Nicholas Piggin <npiggin@gmail.com>
Subject: Re: [PATCH] powerpc/svm: Don't issue ultracalls if
 !mem_encrypt_active()
To: linux-kernel@vger.kernel.org, Will Deacon <will@kernel.org>
References: <20210730114231.23445-1-will@kernel.org>
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Cc: Sachin Sant <sachinp@linux.vnet.ibm.com>,
 Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>, linuxppc-dev@lists.ozlabs.org,
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Excerpts from Will Deacon's message of July 30, 2021 9:42 pm:
> 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.
>=20
> Sachin reports that this leads to the following crash on a Power server:
>=20
> [    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!
>=20
> 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.
>=20
> Cc: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
> Cc: Claire Chang <tientzu@chromium.org>
> Cc: Christoph Hellwig <hch@lst.de>
> Cc: Robin Murphy <robin.murphy@arm.com>
> Fixes: ad6c00283163 ("swiotlb: Free tbl memory in swiotlb_exit()")
> Suggested-by: Nicholas Piggin <npiggin@gmail.com>
> Reported-by: Sachin Sant <sachinp@linux.vnet.ibm.com>
> Tested-by: Sachin Sant <sachinp@linux.vnet.ibm.com>
> Tested-by: Nathan Chancellor <nathan@kernel.org>
> Link: https://lore.kernel.org/r/1905CD70-7656-42AE-99E2-A31FC3812EAC@linu=
x.vnet.ibm.com/
> Signed-off-by: Will Deacon <will@kernel.org>
> ---

Thanks for writing it.

Acked-by: Nicholas Piggin <npiggin@gmail.com>

>  arch/powerpc/platforms/pseries/svm.c | 6 ++++++
>  1 file changed, 6 insertions(+)
>=20
> diff --git a/arch/powerpc/platforms/pseries/svm.c b/arch/powerpc/platform=
s/pseries/svm.c
> index 1d829e257996..87f001b4c4e4 100644
> --- a/arch/powerpc/platforms/pseries/svm.c
> +++ b/arch/powerpc/platforms/pseries/svm.c
> @@ -63,6 +63,9 @@ void __init svm_swiotlb_init(void)
> =20
>  int set_memory_encrypted(unsigned long addr, int numpages)
>  {
> +	if (!mem_encrypt_active())
> +		return 0;
> +
>  	if (!PAGE_ALIGNED(addr))
>  		return -EINVAL;
> =20
> @@ -73,6 +76,9 @@ int set_memory_encrypted(unsigned long addr, int numpag=
es)
> =20
>  int set_memory_decrypted(unsigned long addr, int numpages)
>  {
> +	if (!mem_encrypt_active())
> +		return 0;
> +
>  	if (!PAGE_ALIGNED(addr))
>  		return -EINVAL;
> =20
> --=20
> 2.32.0.554.ge1b32706d8-goog
>=20
>=20