Re: [PATCH] target/riscv/cpu_helper.c: fix wrong exception raise

[Daniel Henrique Barboza]

On 3/29/24 10:45, Alexei Filippov wrote:
> Successed two stage translation, but failed pmp check can cause guest
> page fault instead of regular page fault.
>
> In case of execution ld instuction in VS mode we can
> face situation when two stages of translation was passed successfully,
> and if PMP check was failed first_stage_error variable going to be
> setted to false and raise_mmu_exception will raise
> RISCV_EXCP_LOAD_GUEST_ACCESS_FAULT(scause == 21) instead of
> RISCV_EXCP_LOAD_ACCESS_FAULT(scause == 5) and this is wrong, according
> to RISCV privileged spec sect. 3.7: Attempting to execute a load or
> load-reserved instruction which accesses a physical address within a
> PMP region without read permissions raises a load access-fault
> exception.
>
> Signed-off-by: Alexei Filippov <alexei.filippov@syntacore.com>
> ---
>   target/riscv/cpu_helper.c | 4 +---
>   1 file changed, 1 insertion(+), 3 deletions(-)
>
> diff --git a/target/riscv/cpu_helper.c b/target/riscv/cpu_helper.c
> index bc70ab5abc..eaef1c2c62 100644
> --- a/target/riscv/cpu_helper.c
> +++ b/target/riscv/cpu_helper.c
> @@ -1408,9 +1408,7 @@ bool riscv_cpu_tlb_fill(CPUState *cs, vaddr address, int 
> size,
>                                 __func__, pa, ret, prot_pmp, tlb_size);
>   
>                   prot &= prot_pmp;
> -            }
> -
> -            if (ret != TRANSLATE_SUCCESS) {
> +            } else {


This solves the issue but we're leaving the 'first_stage_error' flag in an 
inconsistent
state - the call for get_physical_address_pmp() inside "if (ret == 
TRANSLATE_SUCCESS)" is
both a PMP error and also a non-first stage error, but now we're leaving it to 
'true'.
Raise raise_mmu_exception() will give the expected PMP fault for the wrong 
reasons, since
it thinks that it's a first-stage fault when it's not. This will work now, but 
any
future change to raise_mmu_exception can break this logic.

I have an internal (not yet sent to review) fix for the same problem. In my 
case I was
supposed to have an INST_ACCESS_FAULT (1) and was getting an 
INST_GUEST_PAGE_FAULT (20).
I'll see if I can send it ASAP so you can have a look and see if it's also good 
for your
problem.



Thanks,

Daniel






>                   /*
>                    * Guest physical address translation failed, this is a HS
>                    * level exception