| Message ID | 20240701145501.761348-1-samuel.holland@sifive.com |
|---|---|
| State | Accepted |
| Headers | show |
| Series | lib: sbi_emulate_csr: Do not log illegal CSR accesses | expand |
On Mon, Jul 1, 2024 at 8:25 PM Samuel Holland <samuel.holland@sifive.com> wrote: > > Illegal CSR accesses from lower privilege modes are delegated to S-mode > and do not necessarily indicate a bug. Supervisor software may want to > emulate some CSRs, or may intentionally disable access to certain > existing CSRs, and thus will expect traps when those CSRs are accessed. > > For example, Linux disables sstatus.VS by default in order to detect > when userspace first accesses vector register state; this includes the > CSRs defined by the V extesion. As a result, if the first vector > instruction in a process is a CSR access, OpenSBI will log the illegal > instruction exception, even though there is no unexpected or erroneous > behavior occurring. > > Since the illegal instruction exception is delegated to S-mode, S-mode > software should be responsible for reporting the exception, not OpenSBI. > > Signed-off-by: Samuel Holland <samuel.holland@sifive.com> LGTM. Reviewed-by: Anup Patel <anup@brainfault.org> Applied this patch to the riscv/opensbi repo. Thanks, Anup > --- > > lib/sbi/sbi_emulate_csr.c | 9 --------- > 1 file changed, 9 deletions(-) > > diff --git a/lib/sbi/sbi_emulate_csr.c b/lib/sbi/sbi_emulate_csr.c > index 5f3b111d..869c81f4 100644 > --- a/lib/sbi/sbi_emulate_csr.c > +++ b/lib/sbi/sbi_emulate_csr.c > @@ -10,7 +10,6 @@ > #include <sbi/riscv_asm.h> > #include <sbi/riscv_encoding.h> > #include <sbi/sbi_bitops.h> > -#include <sbi/sbi_console.h> > #include <sbi/sbi_emulate_csr.h> > #include <sbi/sbi_error.h> > #include <sbi/sbi_hart.h> > @@ -151,10 +150,6 @@ int sbi_emulate_csr_read(int csr_num, struct sbi_trap_regs *regs, > break; > } > > - if (ret) > - sbi_dprintf("%s: hartid%d: invalid csr_num=0x%x\n", > - __func__, current_hartid(), csr_num); > - > return ret; > } > > @@ -189,9 +184,5 @@ int sbi_emulate_csr_write(int csr_num, struct sbi_trap_regs *regs, > break; > } > > - if (ret) > - sbi_dprintf("%s: hartid%d: invalid csr_num=0x%x\n", > - __func__, current_hartid(), csr_num); > - > return ret; > } > -- > 2.44.0 > > > -- > opensbi mailing list > opensbi@lists.infradead.org > http://lists.infradead.org/mailman/listinfo/opensbi
diff --git a/lib/sbi/sbi_emulate_csr.c b/lib/sbi/sbi_emulate_csr.c index 5f3b111d..869c81f4 100644 --- a/lib/sbi/sbi_emulate_csr.c +++ b/lib/sbi/sbi_emulate_csr.c @@ -10,7 +10,6 @@ #include <sbi/riscv_asm.h> #include <sbi/riscv_encoding.h> #include <sbi/sbi_bitops.h> -#include <sbi/sbi_console.h> #include <sbi/sbi_emulate_csr.h> #include <sbi/sbi_error.h> #include <sbi/sbi_hart.h> @@ -151,10 +150,6 @@ int sbi_emulate_csr_read(int csr_num, struct sbi_trap_regs *regs, break; } - if (ret) - sbi_dprintf("%s: hartid%d: invalid csr_num=0x%x\n", - __func__, current_hartid(), csr_num); - return ret; } @@ -189,9 +184,5 @@ int sbi_emulate_csr_write(int csr_num, struct sbi_trap_regs *regs, break; } - if (ret) - sbi_dprintf("%s: hartid%d: invalid csr_num=0x%x\n", - __func__, current_hartid(), csr_num); - return ret; }
Illegal CSR accesses from lower privilege modes are delegated to S-mode and do not necessarily indicate a bug. Supervisor software may want to emulate some CSRs, or may intentionally disable access to certain existing CSRs, and thus will expect traps when those CSRs are accessed. For example, Linux disables sstatus.VS by default in order to detect when userspace first accesses vector register state; this includes the CSRs defined by the V extesion. As a result, if the first vector instruction in a process is a CSR access, OpenSBI will log the illegal instruction exception, even though there is no unexpected or erroneous behavior occurring. Since the illegal instruction exception is delegated to S-mode, S-mode software should be responsible for reporting the exception, not OpenSBI. Signed-off-by: Samuel Holland <samuel.holland@sifive.com> --- lib/sbi/sbi_emulate_csr.c | 9 --------- 1 file changed, 9 deletions(-)