From 6a8d4ca891aa5f9402973eab5d7d9cf3929678b7 Mon Sep 17 00:00:00 2001
From: Haren Myneni <haren@linux.ibm.com>
Date: Mon, 28 Feb 2022 17:13:54 -0800
Subject: [PATCH] powerpc/vas: Map paste address only if window is active

References: jsc#PED-542
Patch-mainline: v5.18-rc1
Git-commit: 6a8d4ca891aa5f9402973eab5d7d9cf3929678b7

The paste address mapping is done with mmap() after the window is
opened with ioctl. The partition has to close VAS windows in the
hypervisor if it lost credits due to DLPAR core removal. But the
kernel marks these windows inactive until the previously lost
credits are available later. If the window is inactive due to
DLPAR after this mmap(), the paste instruction returns failure
until the the OS reopens this window again.

Before the user space issuing mmap(), there is a possibility of
happening DLPAR core removal event which causes the corresponding
window inactive. So if the window is not active, return mmap()
failure with -EACCES and expects the user space reissue mmap()
when the window is active or open a new window when the credit
is available.

Signed-off-by: Haren Myneni <haren@linux.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/bbb203c26b324534e25658cb1dbbcb5160a2f93a.camel@linux.ibm.com
Acked-by: Michal Suchanek <msuchanek@suse.de>
---
 arch/powerpc/platforms/book3s/vas-api.c | 23 ++++++++++++++++++++++-
 1 file changed, 22 insertions(+), 1 deletion(-)

diff --git a/arch/powerpc/platforms/book3s/vas-api.c b/arch/powerpc/platforms/book3s/vas-api.c
index 82f32781c5d2..f9a1615b74da 100644
--- a/arch/powerpc/platforms/book3s/vas-api.c
+++ b/arch/powerpc/platforms/book3s/vas-api.c
@@ -497,10 +497,29 @@ static int coproc_mmap(struct file *fp, struct vm_area_struct *vma)
 		return -EACCES;
 	}
 
+	/*
+	 * The initial mmap is done after the window is opened
+	 * with ioctl. But before mmap(), this window can be closed in
+	 * the hypervisor due to lost credit (core removal on pseries).
+	 * So if the window is not active, return mmap() failure with
+	 * -EACCES and expects the user space reissue mmap() when it
+	 * is active again or open new window when the credit is available.
+	 * mmap_mutex protects the paste address mmap() with DLPAR
+	 * close/open event and allows mmap() only when the window is
+	 * active.
+	 */
+	mutex_lock(&txwin->task_ref.mmap_mutex);
+	if (txwin->status != VAS_WIN_ACTIVE) {
+		pr_err("%s(): Window is not active\n", __func__);
+		rc = -EACCES;
+		goto out;
+	}
+
 	paste_addr = cp_inst->coproc->vops->paste_addr(txwin);
 	if (!paste_addr) {
 		pr_err("%s(): Window paste address failed\n", __func__);
-		return -EINVAL;
+		rc = -EINVAL;
+		goto out;
 	}
 
 	pfn = paste_addr >> PAGE_SHIFT;
@@ -520,6 +539,8 @@ static int coproc_mmap(struct file *fp, struct vm_area_struct *vma)
 	txwin->task_ref.vma = vma;
 	vma->vm_ops = &vas_vm_ops;
 
+out:
+	mutex_unlock(&txwin->task_ref.mmap_mutex);
 	return rc;
 }
 
-- 
2.35.3