From c86edc547692d812d1dcc04220c38310be2c00c3 Mon Sep 17 00:00:00 2001 From: Daniel Henrique Barboza Date: Tue, 21 Jan 2025 14:06:26 -0300 Subject: [PATCH] target/riscv: throw debug exception before page fault In the RISC-V privileged ISA section 3.1.15 table 15, it is determined that a debug exception that is triggered from a load/store has a higher priority than a possible fault that this access might trigger. This is not the case ATM as shown in [1]. Adding a breakpoint in an address that deliberately will fault is causing a load page fault instead of a debug exception. The reason is that we're throwing in the page fault as soon as the fault occurs (end of riscv_cpu_tlb_fill(), raise_mmu_exception()), not allowing the installed watchpoints to trigger. Call cpu_check_watchpoint() in the page fault path to search and execute any watchpoints that might exist for the address, never returning back to the fault path. If no watchpoints are found cpu_check_watchpoint() will return and we'll fall-through the regular path to raise_mmu_exception(). [1] https://gitlab.com/qemu-project/qemu/-/issues/2627 Resolves: https://gitlab.com/qemu-project/qemu/-/issues/2627 Signed-off-by: Daniel Henrique Barboza Reviewed-by: Alistair Francis Reviewed-by: Richard Henderson Message-ID: <20250121170626.1992570-3-dbarboza@ventanamicro.com> Signed-off-by: Alistair Francis --- target/riscv/cpu_helper.c | 18 ++++++++++++++++++ 1 file changed, 18 insertions(+) diff --git a/target/riscv/cpu_helper.c b/target/riscv/cpu_helper.c index 1de8e0e494..29dc721c5d 100644 --- a/target/riscv/cpu_helper.c +++ b/target/riscv/cpu_helper.c @@ -27,6 +27,7 @@ #include "exec/page-protection.h" #include "instmap.h" #include "tcg/tcg-op.h" +#include "hw/core/tcg-cpu-ops.h" #include "trace.h" #include "semihosting/common-semi.h" #include "system/cpu-timers.h" @@ -1697,6 +1698,23 @@ bool riscv_cpu_tlb_fill(CPUState *cs, vaddr address, int size, } else if (probe) { return false; } else { + int wp_access = 0; + + if (access_type == MMU_DATA_LOAD) { + wp_access |= BP_MEM_READ; + } else if (access_type == MMU_DATA_STORE) { + wp_access |= BP_MEM_WRITE; + } + + /* + * If a watchpoint isn't found for 'addr' this will + * be a no-op and we'll resume the mmu_exception path. + * Otherwise we'll throw a debug exception and execution + * will continue elsewhere. + */ + cpu_check_watchpoint(cs, address, size, MEMTXATTRS_UNSPECIFIED, + wp_access, retaddr); + raise_mmu_exception(env, address, access_type, pmp_violation, first_stage_error, two_stage_lookup, two_stage_indirect_error); -- 2.30.2