Re: [PATCH v5 13/20] RISC-V: KVM: Implement stage2 page table programming

Anup Patel
2019-08-22T13:59:00Z

On Thu, Aug 22, 2019 at 6:57 PM Alexander Graf <graf@amazon.com> wrote:
>
>
>
> On 22.08.19 14:38, Anup Patel wrote:
> > On Thu, Aug 22, 2019 at 5:58 PM Alexander Graf <graf@amazon.com> wrote:
> >>
> >> On 22.08.19 10:45, Anup Patel wrote:
> >>> 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.
> >>>
> >>> 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 | 10 +
> >>> arch/riscv/include/asm/pgtable-bits.h | 1 +
> >>> arch/riscv/kvm/mmu.c | 637 +++++++++++++++++++++++++-
> >>> 3 files changed, 638 insertions(+), 10 deletions(-)
> >>>
> >>> diff --git a/arch/riscv/include/asm/kvm_host.h b/arch/riscv/include/asm/kvm_host.h
> >>> index 3b09158f80f2..a37775c92586 100644
> >>> --- a/arch/riscv/include/asm/kvm_host.h
> >>> +++ b/arch/riscv/include/asm/kvm_host.h
> >>> @@ -72,6 +72,13 @@ struct kvm_mmio_decode {
> >>> int shift;
> >>> };
> >>>
> >>> +#define KVM_MMU_PAGE_CACHE_NR_OBJS 32
> >>> +
> >>> +struct kvm_mmu_page_cache {
> >>> + int nobjs;
> >>> + void *objects[KVM_MMU_PAGE_CACHE_NR_OBJS];
> >>> +};
> >>> +
> >>> struct kvm_cpu_context {
> >>> unsigned long zero;
> >>> unsigned long ra;
> >>> @@ -163,6 +170,9 @@ struct kvm_vcpu_arch {
> >>> /* MMIO instruction details */
> >>> struct kvm_mmio_decode mmio_decode;
> >>>
> >>> + /* Cache pages needed to program page tables with spinlock held */
> >>> + struct kvm_mmu_page_cache mmu_page_cache;
> >>> +
> >>> /* VCPU power-off state */
> >>> bool power_off;
> >>>
> >>> diff --git a/arch/riscv/include/asm/pgtable-bits.h b/arch/riscv/include/asm/pgtable-bits.h
> >>> index bbaeb5d35842..be49d62fcc2b 100644
> >>> --- a/arch/riscv/include/asm/pgtable-bits.h
> >>> +++ b/arch/riscv/include/asm/pgtable-bits.h
> >>> @@ -26,6 +26,7 @@
> >>>
> >>> #define _PAGE_SPECIAL _PAGE_SOFT
> >>> #define _PAGE_TABLE _PAGE_PRESENT
> >>> +#define _PAGE_LEAF (_PAGE_READ | _PAGE_WRITE | _PAGE_EXEC)
> >>>
> >>> /*
> >>> * _PAGE_PROT_NONE is set on not-present pages (and ignored by the hardware) to
> >>> diff --git a/arch/riscv/kvm/mmu.c b/arch/riscv/kvm/mmu.c
> >>> index 2b965f9aac07..9e95ab6769f6 100644
> >>> --- a/arch/riscv/kvm/mmu.c
> >>> +++ b/arch/riscv/kvm/mmu.c
> >>> @@ -18,6 +18,432 @@
> >>> #include <asm/page.h>
> >>> #include <asm/pgtable.h>
> >>>
> >>> +#ifdef CONFIG_64BIT
> >>> +#define stage2_have_pmd true
> >>> +#define stage2_gpa_size ((phys_addr_t)(1ULL << 39))
> >>> +#define stage2_cache_min_pages 2
> >>> +#else
> >>> +#define pmd_index(x) 0
> >>> +#define pfn_pmd(x, y) ({ pmd_t __x = { 0 }; __x; })
> >>> +#define stage2_have_pmd false
> >>> +#define stage2_gpa_size ((phys_addr_t)(1ULL << 32))
> >>> +#define stage2_cache_min_pages 1
> >>> +#endif
> >>> +
> >>> +static int stage2_cache_topup(struct kvm_mmu_page_cache *pcache,
> >>> + int min, int max)
> >>> +{
> >>> + void *page;
> >>> +
> >>> + BUG_ON(max > KVM_MMU_PAGE_CACHE_NR_OBJS);
> >>> + if (pcache->nobjs >= min)
> >>> + return 0;
> >>> + while (pcache->nobjs < max) {
> >>> + page = (void *)__get_free_page(GFP_KERNEL | __GFP_ZERO);
> >>> + if (!page)
> >>> + return -ENOMEM;
> >>> + pcache->objects[pcache->nobjs++] = page;
> >>> + }
> >>> +
> >>> + return 0;
> >>> +}
> >>> +
> >>> +static void stage2_cache_flush(struct kvm_mmu_page_cache *pcache)
> >>> +{
> >>> + while (pcache && pcache->nobjs)
> >>> + free_page((unsigned long)pcache->objects[--pcache->nobjs]);
> >>> +}
> >>> +
> >>> +static void *stage2_cache_alloc(struct kvm_mmu_page_cache *pcache)
> >>> +{
> >>> + void *p;
> >>> +
> >>> + if (!pcache)
> >>> + return NULL;
> >>> +
> >>> + BUG_ON(!pcache->nobjs);
> >>> + p = pcache->objects[--pcache->nobjs];
> >>> +
> >>> + return p;
> >>> +}
> >>> +
> >>> +struct local_guest_tlb_info {
> >>> + struct kvm_vmid *vmid;
> >>> + gpa_t addr;
> >>> +};
> >>> +
> >>> +static void local_guest_tlb_flush_vmid_gpa(void *info)
> >>> +{
> >>> + struct local_guest_tlb_info *infop = info;
> >>> +
> >>> + __kvm_riscv_hfence_gvma_vmid_gpa(READ_ONCE(infop->vmid->vmid_version),
> >>> + infop->addr);
> >>> +}
> >>> +
> >>> +static void stage2_remote_tlb_flush(struct kvm *kvm, gpa_t addr)
> >>> +{
> >>> + struct local_guest_tlb_info info;
> >>> + struct kvm_vmid *vmid = &kvm->arch.vmid;
> >>> +
> >>> + /* TODO: This should be SBI call */
> >>> + info.vmid = vmid;
> >>> + info.addr = addr;
> >>> + preempt_disable();
> >>> + smp_call_function_many(cpu_all_mask, local_guest_tlb_flush_vmid_gpa,
> >>> + &info, true);
> >>
> >> This is all nice and dandy on the toy 4 core systems we have today, but
> >> it will become a bottleneck further down the road.
> >>
> >> How many VMIDs do you have? Could you just allocate a new one every time
> >> you switch host CPUs? Then you know exactly which CPUs to flush by
> >> looking at all your vcpu structs and a local field that tells you which
> >> pCPU they're on at this moment.
> >>
> >> Either way, it's nothing that should block inclusion. For today, we're fine.
> >
> > We are not happy about this either.
> >
> > Other two options, we have are:
> > 1. Have SBI calls for remote HFENCEs
> > 2. Propose RISC-V ISA extension for remote FENCEs
> >
> > Option1 is mostly extending SBI spec and implementing it in runtime
> > firmware.
> >
> > Option2 is ideal solution but requires consensus among wider audience
> > in RISC-V foundation.
> >
> > At this point, we are fine with a simple solution.
>
> It's fine to explicitly IPI other CPUs to flush their TLBs. What is not
> fine is to IPI *all* CPUs to flush their TLBs.

Ahh, this should have been cpu_online_mask instead of cpu_all_mask

I will update this in next revision.

Regards,
Anup

>
>
> Alex