From: Ashish Kalra <ashish.kalra@amd.com>

Panic notifiers are invoked with RCU read lock held and when the
SNP panic notifier tries to unregister itself from the panic
notifier callback itself it causes a deadlock as notifier
unregistration does RCU synchronization.

Code flow for SNP panic notifier:
snp_shutdown_on_panic() ->
__sev_firmware_shutdown() ->
__sev_snp_shutdown_locked() ->
atomic_notifier_chain_unregister(.., &snp_panic_notifier)

Fix SNP panic notifier to unregister itself during SNP shutdown
only if panic is not in progress.

Reviewed-by: Tom Lendacky <thomas.lendacky@amd.com>
Cc: stable@vger.kernel.org
Fixes: 19860c3274fb ("crypto: ccp - Register SNP panic notifier only if SNP is enabled")
Signed-off-by: Ashish Kalra <ashish.kalra@amd.com>
---
 drivers/crypto/ccp/sev-dev.c | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/drivers/crypto/ccp/sev-dev.c b/drivers/crypto/ccp/sev-dev.c
index 8fb94c5f006a..17edc6bf5622 100644
--- a/drivers/crypto/ccp/sev-dev.c
+++ b/drivers/crypto/ccp/sev-dev.c
@@ -1787,8 +1787,14 @@ static int __sev_snp_shutdown_locked(int *error, bool panic)
 	sev->snp_initialized = false;
 	dev_dbg(sev->dev, "SEV-SNP firmware shutdown\n");
 
-	atomic_notifier_chain_unregister(&panic_notifier_list,
-					 &snp_panic_notifier);
+	/*
+	 * __sev_snp_shutdown_locked() deadlocks when it tries to unregister
+	 * itself during panic as the panic notifier is called with RCU read
+	 * lock held and notifier unregistration does RCU synchronization.
+	 */
+	if (!panic)
+		atomic_notifier_chain_unregister(&panic_notifier_list,
+						 &snp_panic_notifier);
 
 	/* Reset TMR size back to default */
 	sev_es_tmr_size = SEV_TMR_SIZE;
-- 
2.34.1

On Mon, Jun 16, 2025 at 09:50:27PM +0000, Ashish Kalra wrote:
> From: Ashish Kalra <ashish.kalra@amd.com>
> 
> Panic notifiers are invoked with RCU read lock held and when the
> SNP panic notifier tries to unregister itself from the panic
> notifier callback itself it causes a deadlock as notifier
> unregistration does RCU synchronization.
> 
> Code flow for SNP panic notifier:
> snp_shutdown_on_panic() ->
> __sev_firmware_shutdown() ->
> __sev_snp_shutdown_locked() ->
> atomic_notifier_chain_unregister(.., &snp_panic_notifier)
> 
> Fix SNP panic notifier to unregister itself during SNP shutdown
> only if panic is not in progress.
> 
> Reviewed-by: Tom Lendacky <thomas.lendacky@amd.com>
> Cc: stable@vger.kernel.org
> Fixes: 19860c3274fb ("crypto: ccp - Register SNP panic notifier only if SNP is enabled")
> Signed-off-by: Ashish Kalra <ashish.kalra@amd.com>
> ---
>  drivers/crypto/ccp/sev-dev.c | 10 ++++++++--
>  1 file changed, 8 insertions(+), 2 deletions(-)

Patch applied.  Thanks.
-- 
Email: Herbert Xu <herbert@gondor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt