[PATCH v2 1/5] linux-user/x86_64: Handle the vsyscall page in open_self_maps_{2, 4}

From: Richard Henderson <richard.henderson@linaro.org>
To: qemu-devel@nongnu.org
Cc: laurent@vivier.eu, richard.purdie@linuxfoundation.org,
	mjt@tls.msk.ru, iii@linux.ibm.com
Subject: [PATCH v2 1/5] linux-user/x86_64: Handle the vsyscall page in open_self_maps_{2, 4}
Date: Wed, 28 Feb 2024 10:25:14 -1000	[thread overview]
Message-ID: <20240228202518.33180-2-richard.henderson@linaro.org> (raw)
In-Reply-To: <20240228202518.33180-1-richard.henderson@linaro.org>

This is the only case in which we expect to have no host memory backing
for a guest memory page, because in general linux user processes cannot
map any pages in the top half of the 64-bit address space.

Resolves: https://gitlab.com/qemu-project/qemu/-/issues/2170
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
---
 linux-user/syscall.c | 16 ++++++++++++++++
 1 file changed, 16 insertions(+)

diff --git a/linux-user/syscall.c b/linux-user/syscall.c
index e384e14248..bc8c06522f 100644
--- a/linux-user/syscall.c
+++ b/linux-user/syscall.c
@@ -7994,6 +7994,10 @@ static void open_self_maps_4(const struct open_self_maps_data *d,
         path = "[heap]";
     } else if (start == info->vdso) {
         path = "[vdso]";
+#ifdef TARGET_X86_64
+    } else if (start == TARGET_VSYSCALL_PAGE) {
+        path = "[vsyscall]";
+#endif
     }
 
     /* Except null device (MAP_ANON), adjust offset for this fragment. */
@@ -8082,6 +8086,18 @@ static int open_self_maps_2(void *opaque, target_ulong guest_start,
     uintptr_t host_start = (uintptr_t)g2h_untagged(guest_start);
     uintptr_t host_last = (uintptr_t)g2h_untagged(guest_end - 1);
 
+#ifdef TARGET_X86_64
+    /*
+     * Because of the extremely high position of the page within the guest
+     * virtual address space, this is not backed by host memory at all.
+     * Therefore the loop below would fail.  This is the only instance
+     * of not having host backing memory.
+     */
+    if (guest_start == TARGET_VSYSCALL_PAGE) {
+        return open_self_maps_3(opaque, guest_start, guest_end, flags);
+    }
+#endif
+
     while (1) {
         IntervalTreeNode *n =
             interval_tree_iter_first(d->host_maps, host_start, host_start);
-- 
2.34.1


