Messages in this thread | | | Date | Fri, 22 Jan 2021 09:45:26 +0000 | From | Marc Zyngier <> | Subject | Re: [RFC PATCH] kvm: arm64: Try stage2 block mapping for host device MMIO |
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On 2021-01-22 08:36, Keqian Zhu wrote: > The MMIO region of a device maybe huge (GB level), try to use block > mapping in stage2 to speedup both map and unmap. > > Especially for unmap, it performs TLBI right after each invalidation > of PTE. If all mapping is of PAGE_SIZE, it takes much time to handle > GB level range.
This is only on VM teardown, right? Or do you unmap the device more ofet? Can you please quantify the speedup and the conditions this occurs in?
I have the feeling that we are just circling around another problem, which is that we could rely on a VM-wide TLBI when tearing down the guest. I worked on something like that[1] a long while ago, and parked it for some reason. Maybe it is worth reviving.
[1] https://git.kernel.org/pub/scm/linux/kernel/git/maz/arm-platforms.git/log/?h=kvm-arm64/elide-cmo-tlbi
> > Signed-off-by: Keqian Zhu <zhukeqian1@huawei.com> > --- > arch/arm64/include/asm/kvm_pgtable.h | 11 +++++++++++ > arch/arm64/kvm/hyp/pgtable.c | 15 +++++++++++++++ > arch/arm64/kvm/mmu.c | 12 ++++++++---- > 3 files changed, 34 insertions(+), 4 deletions(-) > > diff --git a/arch/arm64/include/asm/kvm_pgtable.h > b/arch/arm64/include/asm/kvm_pgtable.h > index 52ab38db04c7..2266ac45f10c 100644 > --- a/arch/arm64/include/asm/kvm_pgtable.h > +++ b/arch/arm64/include/asm/kvm_pgtable.h > @@ -82,6 +82,17 @@ struct kvm_pgtable_walker { > const enum kvm_pgtable_walk_flags flags; > }; > > +/** > + * kvm_supported_pgsize() - Get the max supported page size of a > mapping. > + * @pgt: Initialised page-table structure. > + * @addr: Virtual address at which to place the mapping. > + * @end: End virtual address of the mapping. > + * @phys: Physical address of the memory to map. > + * > + * The smallest return value is PAGE_SIZE. > + */ > +u64 kvm_supported_pgsize(struct kvm_pgtable *pgt, u64 addr, u64 end, > u64 phys); > + > /** > * kvm_pgtable_hyp_init() - Initialise a hypervisor stage-1 > page-table. > * @pgt: Uninitialised page-table structure to initialise. > diff --git a/arch/arm64/kvm/hyp/pgtable.c > b/arch/arm64/kvm/hyp/pgtable.c > index bdf8e55ed308..ab11609b9b13 100644 > --- a/arch/arm64/kvm/hyp/pgtable.c > +++ b/arch/arm64/kvm/hyp/pgtable.c > @@ -81,6 +81,21 @@ static bool kvm_block_mapping_supported(u64 addr, > u64 end, u64 phys, u32 level) > return IS_ALIGNED(addr, granule) && IS_ALIGNED(phys, granule); > } > > +u64 kvm_supported_pgsize(struct kvm_pgtable *pgt, u64 addr, u64 end, > u64 phys) > +{ > + u32 lvl; > + u64 pgsize = PAGE_SIZE; > + > + for (lvl = pgt->start_level; lvl < KVM_PGTABLE_MAX_LEVELS; lvl++) { > + if (kvm_block_mapping_supported(addr, end, phys, lvl)) { > + pgsize = kvm_granule_size(lvl); > + break; > + } > + } > + > + return pgsize; > +} > + > static u32 kvm_pgtable_idx(struct kvm_pgtable_walk_data *data, u32 > level) > { > u64 shift = kvm_granule_shift(level); > diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c > index 7d2257cc5438..80b403fc8e64 100644 > --- a/arch/arm64/kvm/mmu.c > +++ b/arch/arm64/kvm/mmu.c > @@ -499,7 +499,8 @@ void kvm_free_stage2_pgd(struct kvm_s2_mmu *mmu) > int kvm_phys_addr_ioremap(struct kvm *kvm, phys_addr_t guest_ipa, > phys_addr_t pa, unsigned long size, bool writable) > { > - phys_addr_t addr; > + phys_addr_t addr, end; > + unsigned long pgsize; > int ret = 0; > struct kvm_mmu_memory_cache cache = { 0, __GFP_ZERO, NULL, }; > struct kvm_pgtable *pgt = kvm->arch.mmu.pgt; > @@ -509,21 +510,24 @@ int kvm_phys_addr_ioremap(struct kvm *kvm, > phys_addr_t guest_ipa, > > size += offset_in_page(guest_ipa); > guest_ipa &= PAGE_MASK; > + end = guest_ipa + size; > > - for (addr = guest_ipa; addr < guest_ipa + size; addr += PAGE_SIZE) { > + for (addr = guest_ipa; addr < end; addr += pgsize) { > ret = kvm_mmu_topup_memory_cache(&cache, > kvm_mmu_cache_min_pages(kvm)); > if (ret) > break; > > + pgsize = kvm_supported_pgsize(pgt, addr, end, pa); > + > spin_lock(&kvm->mmu_lock); > - ret = kvm_pgtable_stage2_map(pgt, addr, PAGE_SIZE, pa, prot, > + ret = kvm_pgtable_stage2_map(pgt, addr, pgsize, pa, prot, > &cache); > spin_unlock(&kvm->mmu_lock); > if (ret) > break; > > - pa += PAGE_SIZE; > + pa += pgsize; > } > > kvm_mmu_free_memory_cache(&cache);
This otherwise looks neat enough.
Thanks,
M. -- Jazz is not dead. It just smells funny...
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