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

On 28/2/24 21:25, Richard Henderson wrote:
> 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

Alternatively "#ifdef TARGET_VSYSCALL_PAGE" like in
i386_tr_translate_insn()?

> +    } else if (start == TARGET_VSYSCALL_PAGE) {
> +        path = "[vsyscall]";
> +#endif

Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>