1 files changed, 19 insertions, 0 deletions

diff --git a/gitlab/issues/target_riscv/host_missing/accel_TCG/1053.toml b/gitlab/issues/target_riscv/host_missing/accel_TCG/1053.toml
new file mode 100644
index 000000000..25ea9481a
--- /dev/null
+++ b/gitlab/issues/target_riscv/host_missing/accel_TCG/1053.toml
@@ -0,0 +1,19 @@
+id = 1053
+title = "Executable PMP regions of size less than 4K always trigger an instruction access fault"
+state = "closed"
+created_at = "2022-06-01T12:51:14.201Z"
+closed_at = "2022-11-06T19:28:00.544Z"
+labels = ["accel: TCG", "target: riscv"]
+url = "https://gitlab.com/qemu-project/qemu/-/issues/1053"
+host-os = "Bare-metal"
+host-arch = "RISC-V"
+qemu-version = "master"
+guest-os = "Bare-metal"
+guest-arch = "RISC-V"
+description = """When configuring a PMP region that is less than 4K in size (Page size), and then trying to execute instructions inside said region, TCG always throws a PMP exception, even though the area allows code execution."""
+reproduce = "n/a"
+additional = """I've debugged the issue already, and it's happening because of the following optimization in TCG:
+
+TCG uses `get_page_addr_code_hostp` in order to try and get the translation cached for a whole page of instructions; if this function is unable to translate a whole page, it's supposed to simply return `-1`, and then the caller is supposed to translate and execute on a per-instruction basis. In this case `get_page_addr_code_hostp` calls `tlb_fill`, which then calls `riscv_cpu_tlb_fill`, which then calls `get_physical_address_pmp` to perform the PMP access checks. When said instructions are covered by a PMP region which is smaller than a page, this check then fails, since PMP regions must cover the whole access in order to allow it. At this point `riscv_cpu_tlb_fill` will see that a PMP fault happened, and since `probe` is set to false by `get_page_addr_code_hostp`, it will throw a RISC-V access fault exception instead of just returning a failure that `get_page_addr_code_hostp` can handle (by only accessing the memory of the specific instruction instead, which will be fully covered by the PMP region).
+
+I haven't tried to fix it myself (my first idea is to simply make `get_page_addr_code_hostp` set the probe flag), since I'm not sure if changing that part of TCG will affect other architectures that I'm not aware of."""