linux-kernel - [PATCH] vt: save/restore unicode screen buffer for alternate screen

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Message-ID: <5o2p6qp3-91pq-0p17-or02-1oors4417ns7@onlyvoer.pbz>
Date: Tue, 27 Jan 2026 17:56:01 -0500 (EST)
From: Nicolas Pitre <npitre@...libre.com>
To: Greg Kroah-Hartman <gregkh@...uxfoundation.org>, 
    Jiri Slaby <jirislaby@...nel.org>, 
    Calixte Pernot <calixte.pernot@...noble-inp.org>
cc: linux-kernel@...r.kernel.org, linux-serial@...r.kernel.org
Subject: [PATCH] vt: save/restore unicode screen buffer for alternate
 screen

The alternate screen support added by commit 23743ba64709 ("vt: add
support for smput/rmput escape codes") only saves and restores the
regular screen buffer (vc_origin), but completely ignores the corresponding
unicode screen buffer (vc_uni_lines) creating a messed-up display.

Add vc_saved_uni_lines to save the unicode screen buffer when entering
the alternate screen, and restore it when leaving. Also ensure proper
cleanup in reset_terminal() and vc_deallocate().

Fixes: 23743ba64709 ("vt: add support for smput/rmput escape codes")
Signed-off-by: Nicolas Pitre <npitre@...libre.com>
---
 drivers/tty/vt/vt.c            | 8 ++++++++
 include/linux/console_struct.h | 1 +
 2 files changed, 9 insertions(+)

diff --git a/drivers/tty/vt/vt.c b/drivers/tty/vt/vt.c
index 59b4b5e126ba..83a285577708 100644
--- a/drivers/tty/vt/vt.c
+++ b/drivers/tty/vt/vt.c
@@ -1345,6 +1345,8 @@ struct vc_data *vc_deallocate(unsigned int currcons)
 			kfree(vc->vc_saved_screen);
 			vc->vc_saved_screen = NULL;
 		}
+		vc_uniscr_free(vc->vc_saved_uni_lines);
+		vc->vc_saved_uni_lines = NULL;
 	}
 	return vc;
 }
@@ -1890,6 +1892,8 @@ static void enter_alt_screen(struct vc_data *vc)
 	vc->vc_saved_screen = kmemdup((u16 *)vc->vc_origin, size, GFP_KERNEL);
 	if (vc->vc_saved_screen == NULL)
 		return;
+	vc->vc_saved_uni_lines = vc->vc_uni_lines;
+	vc->vc_uni_lines = NULL;
 	vc->vc_saved_rows = vc->vc_rows;
 	vc->vc_saved_cols = vc->vc_cols;
 	save_cur(vc);
@@ -1911,6 +1915,8 @@ static void leave_alt_screen(struct vc_data *vc)
 		dest = ((u16 *)vc->vc_origin) + r * vc->vc_cols;
 		memcpy(dest, src, 2 * cols);
 	}
+	vc_uniscr_set(vc, vc->vc_saved_uni_lines);
+	vc->vc_saved_uni_lines = NULL;
 	restore_cur(vc);
 	/* Update the entire screen */
 	if (con_should_update(vc))
@@ -2233,6 +2239,8 @@ static void reset_terminal(struct vc_data *vc, int do_clear)
 	if (vc->vc_saved_screen != NULL) {
 		kfree(vc->vc_saved_screen);
 		vc->vc_saved_screen = NULL;
+		vc_uniscr_free(vc->vc_saved_uni_lines);
+		vc->vc_saved_uni_lines = NULL;
 		vc->vc_saved_rows = 0;
 		vc->vc_saved_cols = 0;
 	}
diff --git a/include/linux/console_struct.h b/include/linux/console_struct.h
index 13b35637bd5a..d5ca855116df 100644
--- a/include/linux/console_struct.h
+++ b/include/linux/console_struct.h
@@ -160,6 +160,7 @@ struct vc_data {
 	struct uni_pagedict **uni_pagedict_loc; /* [!] Location of uni_pagedict variable for this console */
 	u32 **vc_uni_lines;			/* unicode screen content */
 	u16		*vc_saved_screen;
+	u32		**vc_saved_uni_lines;
 	unsigned int	vc_saved_cols;
 	unsigned int	vc_saved_rows;
 	/* additional information is in vt_kern.h */
-- 
2.52.0