RE: [PATCH] target/riscv: raise exception to HS-mode at get_physical_address

[Jiangyifei <jiangyifei@huawei.com>]

> -----Original Message-----
> From: Alistair Francis [mailto:alistair23@gmail.com]
> Sent: Saturday, September 26, 2020 6:24 AM
> To: Jiangyifei <jiangyifei@huawei.com>
> Cc: qemu-devel@nongnu.org Developers <qemu-devel@nongnu.org>; open
> list:RISC-V <qemu-riscv@nongnu.org>; Zhanghailiang
> <zhang.zhanghailiang@huawei.com>; Sagar Karandikar
> <sagark@eecs.berkeley.edu>; Bastian Koppelmann
> <kbastian@mail.uni-paderborn.de>; Zhangxiaofeng (F)
> <victor.zhangxiaofeng@huawei.com>; Alistair Francis
> <Alistair.Francis@wdc.com>; yinyipeng <yinyipeng1@huawei.com>; Palmer
> Dabbelt <palmer@dabbelt.com>; Wubin (H) <wu.wubin@huawei.com>;
> dengkai (A) <dengkai1@huawei.com>
> Subject: Re: [PATCH] target/riscv: raise exception to HS-mode at
> get_physical_address
> 
> On Mon, Aug 24, 2020 at 1:43 AM Yifei Jiang <jiangyifei@huawei.com> wrote:
> >
> > VS-stage translation at get_physical_address needs to translate pte
> > address by G-stage translation. But the G-stage translation error can
> > not be distinguished from VS-stage translation error in
> > riscv_cpu_tlb_fill. On migration, destination needs to rebuild pte,
> > and this G-stage translation error must be handled by HS-mode. So
> > introduce TRANSLATE_STAGE2_FAIL so that riscv_cpu_tlb_fill could
> > distinguish and raise it to HS-mode.
> >
> > Signed-off-by: Yifei Jiang <jiangyifei@huawei.com>
> > Signed-off-by: Yipeng Yin <yinyipeng1@huawei.com>
> 
> Thanks for the patch!
> 
> Sorry for the delay here.
> 
> > ---
> >  target/riscv/cpu.h        |  1 +
> >  target/riscv/cpu_helper.c | 12 ++++++++++--
> >  2 files changed, 11 insertions(+), 2 deletions(-)
> >
> > diff --git a/target/riscv/cpu.h b/target/riscv/cpu.h index
> > a804a5d0ba..8b3b368d6a 100644
> > --- a/target/riscv/cpu.h
> > +++ b/target/riscv/cpu.h
> > @@ -85,6 +85,7 @@ enum {
> >  #define TRANSLATE_FAIL 1
> >  #define TRANSLATE_SUCCESS 0
> >  #define MMU_USER_IDX 3
> > +#define TRANSLATE_G_STAGE_FAIL 4
> >
> >  #define MAX_RISCV_PMPS (16)
> >
> > diff --git a/target/riscv/cpu_helper.c b/target/riscv/cpu_helper.c
> > index fd1d373b6f..1635b09c41 100644
> > --- a/target/riscv/cpu_helper.c
> > +++ b/target/riscv/cpu_helper.c
> > @@ -440,7 +440,10 @@ restart:
> >                                                   mmu_idx,
> false,
> > true);
> >
> >              if (vbase_ret != TRANSLATE_SUCCESS) {
> > -                return vbase_ret;
> > +                env->guest_phys_fault_addr = (base |
> > +                                              (addr &
> > +
> (TARGET_PAGE_SIZE -
> > + 1))) >> 2;
> 
> Can we set guest_phys_fault_addr in riscv_cpu_tlb_fill() instead?

Hi Alistair,

It's not easy to do that. The key is that the wrong address(the `base` variable) is not visible to riscv_cpu_tlb_fill().
Because the wrong address may be from any level of PTE which can't be easily obtained by riscv_cpu_tlb_fill().
The alternative is to add an out parameter in get_physical_address(). But it is not either elegant.
What is your advice?

Best Regards,
Yifei

> 
> > +                return TRANSLATE_G_STAGE_FAIL;
> >              }
> >
> >              pte_addr = vbase + idx * ptesize; @@ -728,12 +731,17 @@
> > bool riscv_cpu_tlb_fill(CPUState *cs, vaddr address, int size,
> >          ret = get_physical_address(env, &pa, &prot, address,
> access_type,
> >                                     mmu_idx, true, true);
> >
> > +        if (ret == TRANSLATE_G_STAGE_FAIL) {
> > +            first_stage_error = false;
> > +            access_type = MMU_DATA_LOAD;
> > +        }
> > +
> >          qemu_log_mask(CPU_LOG_MMU,
> >                        "%s 1st-stage address=%" VADDR_PRIx "
> ret %d physical "
> >                        TARGET_FMT_plx " prot %d\n",
> >                        __func__, address, ret, pa, prot);
> >
> > -        if (ret != TRANSLATE_FAIL) {
> > +        if (ret != TRANSLATE_FAIL && ret != TRANSLATE_G_STAGE_FAIL) {
> 
> Otherwise this patch looks correct.
> 
> Alistair
> 
> >              /* Second stage lookup */
> >              im_address = pa;
> >
> > --
> > 2.19.1
> >
> >
> >