Re: [PATCH v3 2/2] riscv: Cleanup KASAN_VMALLOC support

[Palmer Dabbelt]

On Tue, 30 Mar 2021 02:47:30 PDT (-0700), geert@xxxxxxxxxxxxxx wrote:
> Hi Palmer,
>
> On Tue, Mar 30, 2021 at 7:08 AM Palmer Dabbelt <palmer@xxxxxxxxxxx> wrote:
> > On Sat, 13 Mar 2021 00:45:05 PST (-0800), alex@xxxxxxxx wrote:
> > > When KASAN vmalloc region is populated, there is no userspace process and
> > > the page table in use is swapper_pg_dir, so there is no need to read
> > > SATP. Then we can use the same scheme used by kasan_populate_p*d
> > > functions to go through the page table, which harmonizes the code.
> > >
> > > In addition, make use of set_pgd that goes through all unused page table
> > > levels, contrary to p*d_populate functions, which makes this function work
> > > whatever the number of page table levels.
> > >
> > > Signed-off-by: Alexandre Ghiti <alex@xxxxxxxx>
> > > Reviewed-by: Palmer Dabbelt <palmerdabbelt@xxxxxxxxxx>
> > > ---
> > >  arch/riscv/mm/kasan_init.c | 59 ++++++++++++--------------------------
> > >  1 file changed, 18 insertions(+), 41 deletions(-)
> > >
> > > diff --git a/arch/riscv/mm/kasan_init.c b/arch/riscv/mm/kasan_init.c
> > > index 57bf4ae09361..c16178918239 100644
> > > --- a/arch/riscv/mm/kasan_init.c
> > > +++ b/arch/riscv/mm/kasan_init.c
> > > @@ -11,18 +11,6 @@
> > >  #include <asm/fixmap.h>
> > >  #include <asm/pgalloc.h>
> > >
> > > -static __init void *early_alloc(size_t size, int node)
> > > -{
> > > -     void *ptr = memblock_alloc_try_nid(size, size,
> > > -             __pa(MAX_DMA_ADDRESS), MEMBLOCK_ALLOC_ACCESSIBLE, node);
> > > -
> > > -     if (!ptr)
> > > -             panic("%pS: Failed to allocate %zu bytes align=%zx nid=%d from=%llx\n",
> > > -                     __func__, size, size, node, (u64)__pa(MAX_DMA_ADDRESS));
> > > -
> > > -     return ptr;
> > > -}
> > > -
> > >  extern pgd_t early_pg_dir[PTRS_PER_PGD];
> > >  asmlinkage void __init kasan_early_init(void)
> > >  {
> > > @@ -155,38 +143,27 @@ static void __init kasan_populate(void *start, void *end)
> > >       memset(start, KASAN_SHADOW_INIT, end - start);
> > >  }
> > >
> > > -void __init kasan_shallow_populate(void *start, void *end)
> > > +static void __init kasan_shallow_populate_pgd(unsigned long vaddr, unsigned long end)
> > >  {
> > > -     unsigned long vaddr = (unsigned long)start & PAGE_MASK;
> > > -     unsigned long vend = PAGE_ALIGN((unsigned long)end);
> > > -     unsigned long pfn;
> > > -     int index;
> > > +     unsigned long next;
> > >       void *p;
> > > -     pud_t *pud_dir, *pud_k;
> > > -     pgd_t *pgd_dir, *pgd_k;
> > > -     p4d_t *p4d_dir, *p4d_k;
> > > -
> > > -     while (vaddr < vend) {
> > > -             index = pgd_index(vaddr);
> > > -             pfn = csr_read(CSR_SATP) & SATP_PPN;
> > > -             pgd_dir = (pgd_t *)pfn_to_virt(pfn) + index;
> > > -             pgd_k = init_mm.pgd + index;
> > > -             pgd_dir = pgd_offset_k(vaddr);
> > > -             set_pgd(pgd_dir, *pgd_k);
> > > -
> > > -             p4d_dir = p4d_offset(pgd_dir, vaddr);
> > > -             p4d_k  = p4d_offset(pgd_k, vaddr);
> > > -
> > > -             vaddr = (vaddr + PUD_SIZE) & PUD_MASK;
> > > -             pud_dir = pud_offset(p4d_dir, vaddr);
> > > -             pud_k = pud_offset(p4d_k, vaddr);
> > > -
> > > -             if (pud_present(*pud_dir)) {
> > > -                     p = early_alloc(PAGE_SIZE, NUMA_NO_NODE);
> > > -                     pud_populate(&init_mm, pud_dir, p);
> > > +     pgd_t *pgd_k = pgd_offset_k(vaddr);
> > > +
> > > +     do {
> > > +             next = pgd_addr_end(vaddr, end);
> > > +             if (pgd_page_vaddr(*pgd_k) == (unsigned long)lm_alias(kasan_early_shadow_pmd)) {
> > > +                     p = memblock_alloc(PAGE_SIZE, PAGE_SIZE);
> > > +                     set_pgd(pgd_k, pfn_pgd(PFN_DOWN(__pa(p)), PAGE_TABLE));
> > >               }
> > > -             vaddr += PAGE_SIZE;
> > > -     }
> > > +     } while (pgd_k++, vaddr = next, vaddr != end);
> > > +}
> > > +
> > > +static void __init kasan_shallow_populate(void *start, void *end)
> > > +{
> > > +     unsigned long vaddr = (unsigned long)start & PAGE_MASK;
> > > +     unsigned long vend = PAGE_ALIGN((unsigned long)end);
> > > +
> > > +     kasan_shallow_populate_pgd(vaddr, vend);
> > >
> > >       local_flush_tlb_all();
> > >  }
> >
> > Thanks, this is on for-next.
>
> Your for-next does not include your fixes branch, hence they now conflict,
> and for-next lacks the local_flush_tlb_all().

This came up before and I don't think we ever sorted out what the right 
thing to do is.  Right now I'm keeping for-next pinned an at early RC, 
but fast-forwarding fixes to the latest RC every time I sent a PR.  I 
don't have fixes merged back into for-next because I don't want those 
merges to show up when I send my merge window PRs.

For this one I purposefully left out the local_flush_tlb_all() whene I 
pulled in this patch, and was planning on fixing it up along with any 
other merge conflicts when I send along the PR.  It does all seem like a 
bit of a song and dance here, though, so I'm open to suggestions as to 
how to run this better -- though last time I went through that exercise 
it seemed like everyone had their own way of doing it, they all had a 
different set of issues, and I was at least familiar with this flavor of 
craziness.

I was kind of tempted to convert for-next over into a branch that only 
contains merges, though, which would make it a bit easier to merge fixes 
in.

> Gr{oetje,eeting}s,
>
>                         Geert