RE: [PATCH v15 10/17] RISC-V: KVM: Implement stage2 page table programming

[Jiangyifei <jiangyifei@huawei.com>]

> -----Original Message-----
> From: Anup Patel [mailto:anup@brainfault.org]
> Sent: Monday, November 30, 2020 6:22 PM
> To: Jiangyifei <jiangyifei@huawei.com>
> Cc: Anup Patel <anup.patel@wdc.com>; Palmer Dabbelt
> <palmer@dabbelt.com>; Palmer Dabbelt <palmerdabbelt@google.com>; Paul
> Walmsley <paul.walmsley@sifive.com>; Albert Ou <aou@eecs.berkeley.edu>;
> Paolo Bonzini <pbonzini@redhat.com>; Alexander Graf <graf@amazon.com>;
> Atish Patra <atish.patra@wdc.com>; Alistair Francis
> <Alistair.Francis@wdc.com>; Damien Le Moal <damien.lemoal@wdc.com>;
> kvm@vger.kernel.org; kvm-riscv@lists.infradead.org;
> linux-riscv@lists.infradead.org; linux-kernel@vger.kernel.org; Zhangxiaofeng (F)
> <victor.zhangxiaofeng@huawei.com>; Wubin (H) <wu.wubin@huawei.com>;
> dengkai (A) <dengkai1@huawei.com>; yinyipeng <yinyipeng1@huawei.com>
> Subject: Re: [PATCH v15 10/17] RISC-V: KVM: Implement stage2 page table
> programming
> 
> On Tue, Nov 24, 2020 at 2:56 PM Anup Patel <anup@brainfault.org> wrote:
> >
> > On Mon, Nov 16, 2020 at 2:59 PM Jiangyifei <jiangyifei@huawei.com> wrote:
> > >
> > >
> > > > -----Original Message-----
> > > > From: Anup Patel [mailto:anup.patel@wdc.com]
> > > > Sent: Monday, November 9, 2020 7:33 PM
> > > > To: Palmer Dabbelt <palmer@dabbelt.com>; Palmer Dabbelt
> > > > <palmerdabbelt@google.com>; Paul Walmsley
> > > > <paul.walmsley@sifive.com>; Albert Ou <aou@eecs.berkeley.edu>;
> > > > Paolo Bonzini <pbonzini@redhat.com>
> > > > Cc: Alexander Graf <graf@amazon.com>; Atish Patra
> > > > <atish.patra@wdc.com>; Alistair Francis
> > > > <Alistair.Francis@wdc.com>; Damien Le Moal
> > > > <damien.lemoal@wdc.com>; Anup Patel <anup@brainfault.org>;
> > > > kvm@vger.kernel.org; kvm-riscv@lists.infradead.org;
> > > > linux-riscv@lists.infradead.org; linux-kernel@vger.kernel.org;
> > > > Anup Patel <anup.patel@wdc.com>; Jiangyifei
> > > > <jiangyifei@huawei.com>
> > > > Subject: [PATCH v15 10/17] RISC-V: KVM: Implement stage2 page
> > > > table programming
> > > >
> > > > This patch implements all required functions for programming the
> > > > stage2 page table for each Guest/VM.
> > > >
> > > > At high-level, the flow of stage2 related functions is similar
> > > > from KVM
> > > > ARM/ARM64 implementation but the stage2 page table format is quite
> > > > different for KVM RISC-V.
> > > >
> > > > [jiangyifei: stage2 dirty log support]
> > > > Signed-off-by: Yifei Jiang <jiangyifei@huawei.com>
> > > > Signed-off-by: Anup Patel <anup.patel@wdc.com>
> > > > Acked-by: Paolo Bonzini <pbonzini@redhat.com>
> > > > Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
> > > > ---
> > > >  arch/riscv/include/asm/kvm_host.h     |  12 +
> > > >  arch/riscv/include/asm/pgtable-bits.h |   1 +
> > > >  arch/riscv/kvm/Kconfig                |   1 +
> > > >  arch/riscv/kvm/main.c                 |  19 +
> > > >  arch/riscv/kvm/mmu.c                  | 649
> > > > +++++++++++++++++++++++++-
> > > >  arch/riscv/kvm/vm.c                   |   6 -
> > > >  6 files changed, 672 insertions(+), 16 deletions(-)
> > > >
> > >
> > > ......
> > >
> > > >
> > > >  int kvm_riscv_stage2_map(struct kvm_vcpu *vcpu, @@ -69,27
> > > > +562,163 @@ int kvm_riscv_stage2_map(struct kvm_vcpu *vcpu,
> > > >                        gpa_t gpa, unsigned long hva,
> > > >                        bool writeable, bool is_write)  {
> > > > -     /* TODO: */
> > > > -     return 0;
> > > > +     int ret;
> > > > +     kvm_pfn_t hfn;
> > > > +     short vma_pageshift;
> > > > +     gfn_t gfn = gpa >> PAGE_SHIFT;
> > > > +     struct vm_area_struct *vma;
> > > > +     struct kvm *kvm = vcpu->kvm;
> > > > +     struct kvm_mmu_page_cache *pcache =
> &vcpu->arch.mmu_page_cache;
> > > > +     bool logging = (memslot->dirty_bitmap &&
> > > > +                     !(memslot->flags & KVM_MEM_READONLY)) ?
> true : false;
> > > > +     unsigned long vma_pagesize;
> > > > +
> > > > +     mmap_read_lock(current->mm);
> > > > +
> > > > +     vma = find_vma_intersection(current->mm, hva, hva + 1);
> > > > +     if (unlikely(!vma)) {
> > > > +             kvm_err("Failed to find VMA for hva 0x%lx\n", hva);
> > > > +             mmap_read_unlock(current->mm);
> > > > +             return -EFAULT;
> > > > +     }
> > > > +
> > > > +     if (is_vm_hugetlb_page(vma))
> > > > +             vma_pageshift = huge_page_shift(hstate_vma(vma));
> > > > +     else
> > > > +             vma_pageshift = PAGE_SHIFT;
> > > > +     vma_pagesize = 1ULL << vma_pageshift;
> > > > +     if (logging || (vma->vm_flags & VM_PFNMAP))
> > > > +             vma_pagesize = PAGE_SIZE;
> > > > +
> > > > +     if (vma_pagesize == PMD_SIZE || vma_pagesize == PGDIR_SIZE)
> > > > +             gfn = (gpa & huge_page_mask(hstate_vma(vma))) >>
> > > > + PAGE_SHIFT;
> > > > +
> > > > +     mmap_read_unlock(current->mm);
> > > > +
> > > > +     if (vma_pagesize != PGDIR_SIZE &&
> > > > +         vma_pagesize != PMD_SIZE &&
> > > > +         vma_pagesize != PAGE_SIZE) {
> > > > +             kvm_err("Invalid VMA page size 0x%lx\n",
> vma_pagesize);
> > > > +             return -EFAULT;
> > > > +     }
> > > > +
> > > > +     /* We need minimum second+third level pages */
> > > > +     ret = stage2_cache_topup(pcache, stage2_pgd_levels,
> > > > +
> KVM_MMU_PAGE_CACHE_NR_OBJS);
> > > > +     if (ret) {
> > > > +             kvm_err("Failed to topup stage2 cache\n");
> > > > +             return ret;
> > > > +     }
> > > > +
> > > > +     hfn = gfn_to_pfn_prot(kvm, gfn, is_write, NULL);
> > > > +     if (hfn == KVM_PFN_ERR_HWPOISON) {
> > > > +             send_sig_mceerr(BUS_MCEERR_AR, (void __user *)hva,
> > > > +                             vma_pageshift, current);
> > > > +             return 0;
> > > > +     }
> > > > +     if (is_error_noslot_pfn(hfn))
> > > > +             return -EFAULT;
> > > > +
> > > > +     /*
> > > > +      * If logging is active then we allow writable pages only
> > > > +      * for write faults.
> > > > +      */
> > > > +     if (logging && !is_write)
> > > > +             writeable = false;
> > > > +
> > > > +     spin_lock(&kvm->mmu_lock);
> > > > +
> > > > +     if (writeable) {
> > >
> > > Hi Anup,
> > >
> > > What is the purpose of "writable = !memslot_is_readonly(slot)" in this
> series?
> >
> > Where ? I don't see this line in any of the patches.
> >
> > >
> > > When mapping the HVA to HPA above, it doesn't know that the PTE
> writeable of stage2 is "!memslot_is_readonly(slot)".
> > > This may causes the difference between the writability of HVA->HPA and
> GPA->HPA.
> > > For example, GPA->HPA is writeable, but HVA->HPA is not writeable.
> >
> > Yes, this is possible particularly when Host kernel is updating
> > writability of HVA->HPA mappings for swapping in/out pages.
> >
> > >
> > > Is it better that the writability of HVA->HPA is also determined by whether
> the memslot is readonly in this change?
> > > Like this:
> > > -    hfn = gfn_to_pfn_prot(kvm, gfn, is_write, NULL);
> > > +    hfn = gfn_to_pfn_prot(kvm, gfn, writeable, NULL);
> >
> > The gfn_to_pfn_prot() needs to know what type of fault we got (i.e
> > read/write fault). Rest of the information (such as whether slot is
> > writable or not) is already available to gfn_to_pfn_prot().
> >
> > The question here is should we pass "&writeable" or NULL as last
> > parameter to gfn_to_pfn_prot(). The recent JUMP label support in Linux
> > RISC-V causes problem on HW where PTE 'A' and 'D' bits are not updated
> > by HW so I have to change last parameter of gfn_to_pfn_prot() from
> > "&writeable" to NULL.
> >
> > I am still investigating this.
> 
> This turned-out to be a bug in Spike which is not fixed.
> 
> I will include following change in v16 patch series:
> 
> 
> diff --git a/arch/riscv/include/asm/kvm_host.h
> b/arch/riscv/include/asm/kvm_host.h
> index 241030956d47..dc2666b4180b 100644
> --- a/arch/riscv/include/asm/kvm_host.h
> +++ b/arch/riscv/include/asm/kvm_host.h
> @@ -232,8 +232,7 @@ void __kvm_riscv_hfence_gvma_all(void);
> 
>  int kvm_riscv_stage2_map(struct kvm_vcpu *vcpu,
>               struct kvm_memory_slot *memslot,
> -             gpa_t gpa, unsigned long hva,
> -             bool writeable, bool is_write);
> +             gpa_t gpa, unsigned long hva, bool is_write);
>  void kvm_riscv_stage2_flush_cache(struct kvm_vcpu *vcpu);  int
> kvm_riscv_stage2_alloc_pgd(struct kvm *kvm);  void
> kvm_riscv_stage2_free_pgd(struct kvm *kvm); diff --git
> a/arch/riscv/kvm/mmu.c b/arch/riscv/kvm/mmu.c index
> fcaeadc9b34d..56fda9ef70fd 100644
> --- a/arch/riscv/kvm/mmu.c
> +++ b/arch/riscv/kvm/mmu.c
> @@ -689,11 +689,11 @@ int kvm_test_age_hva(struct kvm *kvm, unsigned
> long hva)
> 
>  int kvm_riscv_stage2_map(struct kvm_vcpu *vcpu,
>               struct kvm_memory_slot *memslot,
> -             gpa_t gpa, unsigned long hva,
> -             bool writeable, bool is_write)
> +             gpa_t gpa, unsigned long hva, bool is_write)
>  {
>      int ret;
>      kvm_pfn_t hfn;
> +    bool writeable;
>      short vma_pageshift;
>      gfn_t gfn = gpa >> PAGE_SHIFT;
>      struct vm_area_struct *vma;
> @@ -742,7 +742,7 @@ int kvm_riscv_stage2_map(struct kvm_vcpu *vcpu,
> 
>      mmu_seq = kvm->mmu_notifier_seq;
> 
> -    hfn = gfn_to_pfn_prot(kvm, gfn, is_write, NULL);
> +    hfn = gfn_to_pfn_prot(kvm, gfn, is_write, &writeable);
>      if (hfn == KVM_PFN_ERR_HWPOISON) {
>          send_sig_mceerr(BUS_MCEERR_AR, (void __user *)hva,
>                  vma_pageshift, current); diff --git
> a/arch/riscv/kvm/vcpu_exit.c b/arch/riscv/kvm/vcpu_exit.c index
> f054406792a6..058cfa168abe 100644
> --- a/arch/riscv/kvm/vcpu_exit.c
> +++ b/arch/riscv/kvm/vcpu_exit.c
> @@ -445,7 +445,7 @@ static int stage2_page_fault(struct kvm_vcpu *vcpu,
> struct kvm_run *run,
>          };
>      }
> 
> -    ret = kvm_riscv_stage2_map(vcpu, memslot, fault_addr, hva, writeable,
> +    ret = kvm_riscv_stage2_map(vcpu, memslot, fault_addr, hva,
>          (trap->scause == EXC_STORE_GUEST_PAGE_FAULT) ? true : false);
>      if (ret < 0)
>          return ret;
> 
> Regards,
> Anup

This change looks good.

Yifei