Re: [PATCH] feat: add loongarch page table walker support for debugger memory access

[Miao Hao]

Hi Bibo,

Thanks for your review. I apologize for my late respond due to some 
personal reasons.

On 2024/12/19 17:57, bibo mao wrote:
> Hi Miao,
>
> Thanks for doing this. It is useful to debug VM.
>
> On 2024/12/19 上午11:24, Miao Hao wrote:
> > Signed-off-by: Miao Hao <haomiao23s@ict.ac.cn>
> > ---
> >   target/loongarch/cpu_helper.c     | 104 ++++++++++++++++++++++++++++--
> >   target/loongarch/internals.h      |   4 +-
> >   target/loongarch/tcg/tlb_helper.c |   4 +-
> >   3 files changed, 104 insertions(+), 8 deletions(-)
> >
> > diff --git a/target/loongarch/cpu_helper.c 
> > b/target/loongarch/cpu_helper.c
> > index 580362ac3e..c0828a813d 100644
> > --- a/target/loongarch/cpu_helper.c
> > +++ b/target/loongarch/cpu_helper.c
> > @@ -141,9 +141,95 @@ bool loongarch_tlb_search(CPULoongArchState 
> > *env, target_ulong vaddr,
> >       return false;
> >   }
> >   +static int loongarch_page_table_walker(CPULoongArchState *env, 
> > hwaddr *physical,
> > +                                 int *prot, target_ulong address)
> > +{
> > +    CPUState *cs = env_cpu(env);
> > +    target_ulong index, phys;
> > +    int shift;
> > +    uint64_t dir_base, dir_width;
> > +    uint64_t base;
> > +    int level;
> > +
> > +    /* 0:64bit, 1:128bit, 2:192bit, 3:256bit */
> > +    shift = FIELD_EX64(env->CSR_PWCL, CSR_PWCL, PTEWIDTH);
> > +    shift = (shift + 1) * 3;

the assignment of variable shift and the corresponding comment is 
incorrect here, and details are logged in the v1.03 change log of 
LoongArch specification volume1 
(https://loongson.cn/uploads/images/2023102309132647981.%E9%BE%99%E8%8A%AF%E6%9E%B6%E6%9E%84%E5%8F%82%E8%80%83%E6%89%8B%E5%86%8C%E5%8D%B7%E4%B8%80_r1p10.pdf)

    /* 0:64bit, 1:128bit, 2:256bit, 3:512bit */
    shift = FIELD_EX64(env->CSR_PWCL, CSR_PWCL, PTEWIDTH);
    shift = shift + 3;

> > +
> > +    if ((address >> 63) & 0x1) {
> > +        base = env->CSR_PGDH;
> > +    } else {
> > +        base = env->CSR_PGDL;
> > +    }
> > +    base &= TARGET_PHYS_MASK;
> > +
> > +    for (level = 4; level > 0; level--) {
> > +        get_dir_base_width(env, &dir_base, &dir_width, level);
> > +
> > +        if (dir_width != 0) {
> how about check whether it equeal to 0 firstly like this?
>            if (dir_width == 0)
>                continue;
It's good to reduce code nesting, I will adopt this suggestion.
> > +            /* get next level page directory */
> > +            index = (address >> dir_base) & ((1 << dir_width) - 1);
> > +            phys = base | index << shift;
> Here will only load first 64bit if shift is not 0, such as 1:128bit, 
> 2:192bit, 3:256bit
After fixing the assignment of shift, this issue no longer exists. Shift 
is less than or equal to 6, and index is 6 bit. Thus, index << shift is 
at most 12 bit.

> > +            base = ldq_phys(cs->as, phys) & TARGET_PHYS_MASK;
> > +            if (!FIELD_EX64(base, TLBENTRY, HUGE)) {
> > +                /* mask off page dir permission bits */
> > +                base &= TARGET_PAGE_MASK;
> > +            } else {
> > +                /* base is a huge pte */
> > +                break;
> > +            }
> > +
> > +            if (base == 0) {
> physical adddress 0 is valid and Valid bit will be checked in later. 
> Can we remove this?
the value of base equals to 0 means that the current page directory 
entry does not point to next level page directory, so we return here
> > +                return TLBRET_NOMATCH;
> > +            }
>
> > +        }
> > +    }
> > +
> > +    /* pte */
> > +    if (FIELD_EX64(base, TLBENTRY, HUGE)) {
> > +        /* Huge Page. base is pte */
> > +        base = FIELD_DP64(base, TLBENTRY, LEVEL, 0);
> > +        base = FIELD_DP64(base, TLBENTRY, HUGE, 0);
> > +        if (FIELD_EX64(base, TLBENTRY, HGLOBAL)) {
> > +            base = FIELD_DP64(base, TLBENTRY, HGLOBAL, 0);
> > +            base = FIELD_DP64(base, TLBENTRY, G, 1);
> > +        }
> > +    } else {
> > +        /* Normal Page. base points to pte */
> > +        get_dir_base_width(env, &dir_base, &dir_width, 0);
> > +        index = (address >> dir_base) & ((1 << dir_width) - 1);
> > +        phys = base | index << shift;
> Ditto, shift may be wider than 64-bit.
>
> Regards
> Bibo Mao

Ditto, shift is less than or equal to 6.


Regards

Miao Hao

> > +        base = ldq_phys(cs->as, phys);
> > +    }
> > +
> > +    /* TODO: check plv and other bits? */
> > +
> > +    /* base is pte, in normal pte format */
> > +    if (!FIELD_EX64(base, TLBENTRY, V)) {
> > +        return TLBRET_NOMATCH;
> > +    }
> > +
> > +    if (!FIELD_EX64(base, TLBENTRY, D)) {
> > +        *prot = PAGE_READ;
> > +    } else {
> > +        *prot = PAGE_READ | PAGE_WRITE;
> > +    }
> > +
> > +    /* get TARGET_PAGE_SIZE aligned physical address */
> > +    base += (address & TARGET_PHYS_MASK) & ((1 << dir_base) - 1);
> > +    /* mask RPLV, NX, NR bits */
> > +    base = FIELD_DP64(base, TLBENTRY_64, RPLV, 0);
> > +    base = FIELD_DP64(base, TLBENTRY_64, NX, 0);
> > +    base = FIELD_DP64(base, TLBENTRY_64, NR, 0);
> > +    /* mask other attribute bits */
> > +    *physical = base & TARGET_PAGE_MASK;
> > +
> > +    return 0;
> > +}
> > +
> >   static int loongarch_map_address(CPULoongArchState *env, hwaddr 
> > *physical,
> >                                    int *prot, target_ulong address,
> > -                                 MMUAccessType access_type, int 
> > mmu_idx)
> > +                                 MMUAccessType access_type, int 
> > mmu_idx,
> > +                                 int is_debug)
> >   {
> >       int index, match;
> >   @@ -151,6 +237,13 @@ static int 
> > loongarch_map_address(CPULoongArchState *env, hwaddr *physical,
> >       if (match) {
> >           return loongarch_map_tlb_entry(env, physical, prot,
> >                                          address, access_type, index, 
> > mmu_idx);
> > +    } else if (is_debug) {
> > +        /*
> > +         * For debugger memory access, we want to do the map when 
> > there is a
> > +         * legal mapping, even if the mapping is not yet in TLB. 
> > return 0 if
> > +         * there is a valid map, else none zero.
> > +         */
> > +        return loongarch_page_table_walker(env, physical, prot, 
> > address);
> >       }
> >         return TLBRET_NOMATCH;
> > @@ -158,7 +251,8 @@ static int 
> > loongarch_map_address(CPULoongArchState *env, hwaddr *physical,
> >   #else
> >   static int loongarch_map_address(CPULoongArchState *env, hwaddr 
> > *physical,
> >                                    int *prot, target_ulong address,
> > -                                 MMUAccessType access_type, int 
> > mmu_idx)
> > +                                 MMUAccessType access_type, int 
> > mmu_idx,
> > +                                 int is_debug)
> >   {
> >       return TLBRET_NOMATCH;
> >   }
> > @@ -178,7 +272,7 @@ static hwaddr dmw_va2pa(CPULoongArchState *env, 
> > target_ulong va,
> >     int get_physical_address(CPULoongArchState *env, hwaddr *physical,
> >                            int *prot, target_ulong address,
> > -                         MMUAccessType access_type, int mmu_idx)
> > +                         MMUAccessType access_type, int mmu_idx, int 
> > is_debug)
> >   {
> >       int user_mode = mmu_idx == MMU_USER_IDX;
> >       int kernel_mode = mmu_idx == MMU_KERNEL_IDX;
> > @@ -222,7 +316,7 @@ int get_physical_address(CPULoongArchState *env, 
> > hwaddr *physical,
> >         /* Mapped address */
> >       return loongarch_map_address(env, physical, prot, address,
> > -                                 access_type, mmu_idx);
> > +                                 access_type, mmu_idx, is_debug);
> >   }
> >     hwaddr loongarch_cpu_get_phys_page_debug(CPUState *cs, vaddr addr)
> > @@ -232,7 +326,7 @@ hwaddr loongarch_cpu_get_phys_page_debug(CPUState 
> > *cs, vaddr addr)
> >       int prot;
> >         if (get_physical_address(env, &phys_addr, &prot, addr, 
> > MMU_DATA_LOAD,
> > -                             cpu_mmu_index(cs, false)) != 0) {
> > +                             cpu_mmu_index(cs, false), 1) != 0) {
> >           return -1;
> >       }
> >       return phys_addr;