Re: [PATCH v2 4/4] swiotlb: Free tbl memory in swiotlb_exit()

From: Guenter Roeck
Date: Sun Aug 01 2021 - 00:59:59 EST

On 7/31/21 7:29 PM, Konrad Rzeszutek Wilk wrote:
On Sat, Jul 31, 2021 at 11:26:11AM -0700, Guenter Roeck wrote:

On Tue, Jul 20, 2021 at 02:38:26PM +0100, Will Deacon wrote:
Although swiotlb_exit() frees the 'slots' metadata array referenced by
'io_tlb_default_mem', it leaves the underlying buffer pages allocated
despite no longer being usable.

Extend swiotlb_exit() to free the buffer pages as well as the slots

This patch causes qemu pseries emulations to crash. Backtrace and bisect
log see below. Reverting it fixes the problem.

I am 99% sure it is fixed by this patch (which should be in linux-next
in 5 minutes):

Yes, it does.


Tested-by: Guenter Roeck <linux@xxxxxxxxxxxx>


From a449ffaf9181b5a2dc705d8a06b13e0068207fd4 Mon Sep 17 00:00:00 2001
From: Will Deacon <will@xxxxxxxxxx>
Date: Fri, 30 Jul 2021 12:42:31 +0100
Subject: [PATCH] powerpc/svm: Don't issue ultracalls if !mem_encrypt_active()

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@xxxxxxxxxx>
Cc: Claire Chang <tientzu@xxxxxxxxxxxx>
Cc: Christoph Hellwig <hch@xxxxxx>
Cc: Robin Murphy <robin.murphy@xxxxxxx>
Fixes: ad6c00283163 ("swiotlb: Free tbl memory in swiotlb_exit()")
Suggested-by: Nicholas Piggin <npiggin@xxxxxxxxx>
Reported-by: Sachin Sant <sachinp@xxxxxxxxxxxxxxxxxx>
Tested-by: Sachin Sant <sachinp@xxxxxxxxxxxxxxxxxx>
Tested-by: Nathan Chancellor <nathan@xxxxxxxxxx>
Signed-off-by: Will Deacon <will@xxxxxxxxxx>
Signed-off-by: Konrad Rzeszutek Wilk <konrad@xxxxxxxxxx>
arch/powerpc/platforms/pseries/svm.c | 6 ++++++
1 file changed, 6 insertions(+)

diff --git a/arch/powerpc/platforms/pseries/svm.c b/arch/powerpc/platforms/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)
int set_memory_encrypted(unsigned long addr, int numpages)
+ if (!mem_encrypt_active())
+ return 0;
if (!PAGE_ALIGNED(addr))
return -EINVAL;
@@ -73,6 +76,9 @@ int set_memory_encrypted(unsigned long addr, int numpages)
int set_memory_decrypted(unsigned long addr, int numpages)
+ if (!mem_encrypt_active())
+ return 0;
if (!PAGE_ALIGNED(addr))
return -EINVAL;