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

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Date:   Fri, 30 Jul 2021 12:42:31 +0100
From:   Will Deacon <will@...nel.org>
To:     linux-kernel@...r.kernel.org
Cc:     iommu@...ts.linux-foundation.org, linuxppc-dev@...ts.ozlabs.org,
        Will Deacon <will@...nel.org>,
        Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
        Claire Chang <tientzu@...omium.org>,
        Christoph Hellwig <hch@....de>,
        Robin Murphy <robin.murphy@....com>,
        Nicholas Piggin <npiggin@...il.com>,
        Sachin Sant <sachinp@...ux.vnet.ibm.com>,
        Nathan Chancellor <nathan@...nel.org>
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@...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(+)

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;
 
-- 
2.32.0.554.ge1b32706d8-goog