qemu-kvm/SOURCES/kvm-backends-iommufd-Remove-mutex.patch

From 92aff3cc1a412de01e9563802fa48848eae5283f Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?C=C3=A9dric=20Le=20Goater?= <clg@redhat.com>
Date: Thu, 21 Dec 2023 16:58:41 +0100
Subject: [PATCH 065/101] backends/iommufd: Remove mutex
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RH-Author: Eric Auger <eric.auger@redhat.com>
RH-MergeRequest: 211: IOMMUFD backend backport
RH-Jira: RHEL-19302 RHEL-21057
RH-Acked-by: Cédric Le Goater <clg@redhat.com>
RH-Acked-by: Sebastian Ott <sebott@redhat.com>
RH-Commit: [64/67] 65518432b18f18ceadafe1b0698cdaa962e84f61 (eauger1/centos-qemu-kvm)

Coverity reports a concurrent data access violation because be->users
is being accessed in iommufd_backend_can_be_deleted() without holding
the mutex.

However, these routines are called from the QEMU main thread when a
device is created. In this case, the code paths should be protected by
the BQL lock and it should be safe to drop the IOMMUFD backend mutex.
Simply remove it.

Fixes: CID 1531550
Fixes: CID 1531549
Reviewed-by: Eric Auger <eric.auger@redhat.com>
Reviewed-by: Zhenzhong Duan <zhenzhong.duan@intel.com>
Signed-off-by: Cédric Le Goater <clg@redhat.com>
(cherry picked from commit 19368b1905b4b917e915526fcbd5bfa3f7439451)
Signed-off-by: Eric Auger <eric.auger@redhat.com>
---
 backends/iommufd.c       | 7 -------
 include/sysemu/iommufd.h | 2 --
 2 files changed, 9 deletions(-)

diff --git a/backends/iommufd.c b/backends/iommufd.c
index 393c0d9a37..1ef683c7b0 100644
--- a/backends/iommufd.c
+++ b/backends/iommufd.c
@@ -29,7 +29,6 @@ static void iommufd_backend_init(Object *obj)
     be->fd = -1;
     be->users = 0;
     be->owned = true;
-    qemu_mutex_init(&be->lock);
 }
 
 static void iommufd_backend_finalize(Object *obj)
@@ -52,10 +51,8 @@ static void iommufd_backend_set_fd(Object *obj, const char *str, Error **errp)
         error_prepend(errp, "Could not parse remote object fd %s:", str);
         return;
     }
-    qemu_mutex_lock(&be->lock);
     be->fd = fd;
     be->owned = false;
-    qemu_mutex_unlock(&be->lock);
     trace_iommu_backend_set_fd(be->fd);
 }
 
@@ -79,7 +76,6 @@ int iommufd_backend_connect(IOMMUFDBackend *be, Error **errp)
 {
     int fd, ret = 0;
 
-    qemu_mutex_lock(&be->lock);
     if (be->owned && !be->users) {
         fd = qemu_open_old("/dev/iommu", O_RDWR);
         if (fd < 0) {
@@ -93,13 +89,11 @@ int iommufd_backend_connect(IOMMUFDBackend *be, Error **errp)
 out:
     trace_iommufd_backend_connect(be->fd, be->owned,
                                   be->users, ret);
-    qemu_mutex_unlock(&be->lock);
     return ret;
 }
 
 void iommufd_backend_disconnect(IOMMUFDBackend *be)
 {
-    qemu_mutex_lock(&be->lock);
     if (!be->users) {
         goto out;
     }
@@ -110,7 +104,6 @@ void iommufd_backend_disconnect(IOMMUFDBackend *be)
     }
 out:
     trace_iommufd_backend_disconnect(be->fd, be->users);
-    qemu_mutex_unlock(&be->lock);
 }
 
 int iommufd_backend_alloc_ioas(IOMMUFDBackend *be, uint32_t *ioas_id,
diff --git a/include/sysemu/iommufd.h b/include/sysemu/iommufd.h
index 9c5524b0ed..9af27ebd6c 100644
--- a/include/sysemu/iommufd.h
+++ b/include/sysemu/iommufd.h
@@ -2,7 +2,6 @@
 #define SYSEMU_IOMMUFD_H
 
 #include "qom/object.h"
-#include "qemu/thread.h"
 #include "exec/hwaddr.h"
 #include "exec/cpu-common.h"
 
@@ -19,7 +18,6 @@ struct IOMMUFDBackend {
     /*< protected >*/
     int fd;            /* /dev/iommu file descriptor */
     bool owned;        /* is the /dev/iommu opened internally */
-    QemuMutex lock;
     uint32_t users;
 
     /*< public >*/
-- 
2.39.3