[PATCH v4 01/10] KVM: arm64: Add snapshot interface for the host stage-2 pagetable
Sebastian Ene
sebastianene at google.com
Tue Dec 19 03:44:10 PST 2023
On Mon, Dec 18, 2023 at 01:58:51PM +0000, Sebastian Ene wrote:
> Introduce a new hvc that allows the pKVM hypervisor to snapshot the host
> stage-2 pagetables. The caller is expected to allocate & free the memory
> for the pagetable snapshot. The below diagram shows the sequence of
> events.
>
> [--- HOST ---]
> (1) allocate memory for the snapshot
> (2) invoke the __pkvm_copy_host_stage2(snapshot) interface
> |____
> [--- HYP ---]
> (3) donate the snapshot from HOST -> HYP
> (4) save the host stage-2 pagetables in the snapshot
> (5) donate the snapshot from HYP -> HOST
> [--- return from HYP ---]
> [--- HOST ---]
> (6) free the memory for the snapshot
>
> When the host kernel invokes this interface, the memory is donated from
> the host to the hypervisor. By doing this the memory is unmapped from the
> host's translation regime to prevent the host from modifying the buffer
> while the hypervisor uses it. The hypervisor walks the host stage-2
> pagetable copy while re-creating the original mappings. When the copying
> is done, the memory is donated from the hypervisor back to the host.
> The pages that have been used from the memcache are donated back to the
> host from a temporary array. The hvc is executing synchronously and the
> preemption is disabled for the current CPU while running inside the
> hypervisor so calling this interface blocks the current CPU until the
> snapshoting is done.
>
> Signed-off-by: Sebastian Ene <sebastianene at google.com>
> ---
> arch/arm64/include/asm/kvm_asm.h | 1 +
> arch/arm64/include/asm/kvm_pgtable.h | 43 ++++
> arch/arm64/kvm/hyp/include/nvhe/mem_protect.h | 1 +
> arch/arm64/kvm/hyp/nvhe/hyp-main.c | 12 ++
> arch/arm64/kvm/hyp/nvhe/mem_protect.c | 186 ++++++++++++++++++
> arch/arm64/kvm/hyp/pgtable.c | 43 ++++
> 6 files changed, 286 insertions(+)
>
> diff --git a/arch/arm64/include/asm/kvm_asm.h b/arch/arm64/include/asm/kvm_asm.h
> index 24b5e6b23..9df3367d8 100644
> --- a/arch/arm64/include/asm/kvm_asm.h
> +++ b/arch/arm64/include/asm/kvm_asm.h
> @@ -81,6 +81,7 @@ enum __kvm_host_smccc_func {
> __KVM_HOST_SMCCC_FUNC___pkvm_init_vm,
> __KVM_HOST_SMCCC_FUNC___pkvm_init_vcpu,
> __KVM_HOST_SMCCC_FUNC___pkvm_teardown_vm,
> + __KVM_HOST_SMCCC_FUNC___pkvm_host_stage2_snapshot,
> };
>
> #define DECLARE_KVM_VHE_SYM(sym) extern char sym[]
> diff --git a/arch/arm64/include/asm/kvm_pgtable.h b/arch/arm64/include/asm/kvm_pgtable.h
> index d3e354bb8..f73efd8a8 100644
> --- a/arch/arm64/include/asm/kvm_pgtable.h
> +++ b/arch/arm64/include/asm/kvm_pgtable.h
> @@ -10,6 +10,7 @@
> #include <linux/bits.h>
> #include <linux/kvm_host.h>
> #include <linux/types.h>
> +#include <asm/kvm_host.h>
>
> #define KVM_PGTABLE_MAX_LEVELS 4U
>
> @@ -351,6 +352,28 @@ struct kvm_pgtable {
> kvm_pgtable_force_pte_cb_t force_pte_cb;
> };
>
> +/**
> + * struct kvm_pgtable_snapshot - Snapshot page-table wrapper.
> + * @pgtable: The page-table configuration.
> + * @mc: Memcache used for pagetable pages allocation.
> + * @pgd_hva: Host virtual address of a physically contiguous buffer
> + * used for storing the PGD.
> + * @pgd_pages: The size of the phyisically contiguous buffer in pages.
> + * @used_pages_hva: Host virtual address of a physically contiguous buffer
> + * used for storing the consumed pages from the memcache.
> + * @num_used_pages The size of the used buffer in pages.
> + * @used_pages_indx The current index of the used pages array.
> + */
> +struct kvm_pgtable_snapshot {
> + struct kvm_pgtable pgtable;
> + struct kvm_hyp_memcache mc;
> + void *pgd_hva;
> + size_t pgd_pages;
> + phys_addr_t *used_pages_hva;
> + size_t num_used_pages;
> + size_t used_pages_indx;
> +};
> +
> /**
> * kvm_pgtable_hyp_init() - Initialise a hypervisor stage-1 page-table.
> * @pgt: Uninitialised page-table structure to initialise.
> @@ -756,4 +779,24 @@ enum kvm_pgtable_prot kvm_pgtable_hyp_pte_prot(kvm_pte_t pte);
> */
> void kvm_tlb_flush_vmid_range(struct kvm_s2_mmu *mmu,
> phys_addr_t addr, size_t size);
> +
> +#ifdef CONFIG_NVHE_EL2_DEBUG
> +/**
> + * kvm_pgtable_stage2_snapshot() - Given a memcache and a destination
> + * pagetable where we have the original PGD
> + * copied, build a snapshot table with page table
> + * pages from the given memcache.
> + *
> + * @to_pgt: Destination pagetable
> + * @mc: The memcache where we allocate the destination pagetables from
> + */
> +int kvm_pgtable_stage2_snapshot(struct kvm_pgtable *to_pgt,
> + void *mc);
> +#else
> +static inline int kvm_pgtable_stage2_snapshot(struct kvm_pgtable *to_pgt,
> + void *mc)
> +{
> + return -EPERM;
> +}
> +#endif /* CONFIG_NVHE_EL2_DEBUG */
> #endif /* __ARM64_KVM_PGTABLE_H__ */
> diff --git a/arch/arm64/kvm/hyp/include/nvhe/mem_protect.h b/arch/arm64/kvm/hyp/include/nvhe/mem_protect.h
> index 0972faccc..ca8f76915 100644
> --- a/arch/arm64/kvm/hyp/include/nvhe/mem_protect.h
> +++ b/arch/arm64/kvm/hyp/include/nvhe/mem_protect.h
> @@ -69,6 +69,7 @@ int __pkvm_host_donate_hyp(u64 pfn, u64 nr_pages);
> int __pkvm_hyp_donate_host(u64 pfn, u64 nr_pages);
> int __pkvm_host_share_ffa(u64 pfn, u64 nr_pages);
> int __pkvm_host_unshare_ffa(u64 pfn, u64 nr_pages);
> +int __pkvm_host_stage2_snapshot(struct kvm_pgtable_snapshot *snapshot);
>
> bool addr_is_memory(phys_addr_t phys);
> int host_stage2_idmap_locked(phys_addr_t addr, u64 size, enum kvm_pgtable_prot prot);
> diff --git a/arch/arm64/kvm/hyp/nvhe/hyp-main.c b/arch/arm64/kvm/hyp/nvhe/hyp-main.c
> index 2385fd03e..7b215245f 100644
> --- a/arch/arm64/kvm/hyp/nvhe/hyp-main.c
> +++ b/arch/arm64/kvm/hyp/nvhe/hyp-main.c
> @@ -314,6 +314,17 @@ static void handle___pkvm_teardown_vm(struct kvm_cpu_context *host_ctxt)
> cpu_reg(host_ctxt, 1) = __pkvm_teardown_vm(handle);
> }
>
> +static void handle___pkvm_host_stage2_snapshot(struct kvm_cpu_context *host_ctxt)
> +{
> +#ifdef CONFIG_NVHE_EL2_DEBUG
> + DECLARE_REG(struct kvm_pgtable_snapshot *, snapshot_hva, host_ctxt, 1);
> +
> + cpu_reg(host_ctxt, 1) = __pkvm_host_stage2_snapshot(snapshot_hva);
> +#else
> + cpu_reg(host_ctxt, 0) = SMCCC_RET_NOT_SUPPORTED;
> +#endif
> +}
> +
> typedef void (*hcall_t)(struct kvm_cpu_context *);
>
> #define HANDLE_FUNC(x) [__KVM_HOST_SMCCC_FUNC_##x] = (hcall_t)handle_##x
> @@ -348,6 +359,7 @@ static const hcall_t host_hcall[] = {
> HANDLE_FUNC(__pkvm_init_vm),
> HANDLE_FUNC(__pkvm_init_vcpu),
> HANDLE_FUNC(__pkvm_teardown_vm),
> + HANDLE_FUNC(__pkvm_host_stage2_snapshot),
> };
>
> static void handle_host_hcall(struct kvm_cpu_context *host_ctxt)
> diff --git a/arch/arm64/kvm/hyp/nvhe/mem_protect.c b/arch/arm64/kvm/hyp/nvhe/mem_protect.c
> index 8d0a5834e..aaf07f9e1 100644
> --- a/arch/arm64/kvm/hyp/nvhe/mem_protect.c
> +++ b/arch/arm64/kvm/hyp/nvhe/mem_protect.c
> @@ -266,6 +266,192 @@ int kvm_guest_prepare_stage2(struct pkvm_hyp_vm *vm, void *pgd)
> return 0;
> }
>
> +#ifdef CONFIG_NVHE_EL2_DEBUG
> +static void *snap_zalloc_page(void *mc)
> +{
> + struct hyp_page *p;
> + void *addr;
> + struct kvm_pgtable_snapshot *snap;
> + phys_addr_t *used_pg;
> +
> + snap = container_of(mc, struct kvm_pgtable_snapshot, mc);
> + used_pg = kern_hyp_va(snap->used_pages_hva);
> +
> + /* Check if we have space to track the used page */
> + if (snap->used_pages_indx * sizeof(phys_addr_t) > snap->num_used_pages * PAGE_SIZE)
This should be '>=' instead, and I will fix this.
> + return NULL;
> +
> + addr = pop_hyp_memcache(mc, hyp_phys_to_virt);
> + if (!addr)
> + return addr;
> + used_pg[snap->used_pages_indx++] = hyp_virt_to_phys(addr);
> +
> + memset(addr, 0, PAGE_SIZE);
> + p = hyp_virt_to_page(addr);
> + memset(p, 0, sizeof(*p));
> +
> + return addr;
> +}
> +
> +static void snap_free_pages_exact(void *addr, unsigned long size)
> +{
> + u8 order = get_order(size);
> + unsigned int i;
> + struct hyp_page *p;
> +
> + for (i = 0; i < (1 << order); i++) {
> + p = hyp_virt_to_page(addr + (i * PAGE_SIZE));
> + hyp_page_ref_dec(p);
> + }
> +}
> +
> +static void *pkvm_setup_snapshot(struct kvm_pgtable_snapshot *snap_hva)
> +{
> + unsigned long i;
> + void *pgd, *used_pg;
> + phys_addr_t mc_page, next_mc_page;
> + struct kvm_pgtable_snapshot *snap;
> +
> + snap = (void *)kern_hyp_va(snap_hva);
> + if (!PAGE_ALIGNED(snap))
> + return NULL;
> +
> + if (__pkvm_host_donate_hyp(hyp_virt_to_pfn(snap), 1))
> + return NULL;
> +
> + pgd = kern_hyp_va(snap->pgd_hva);
> + if (!PAGE_ALIGNED(pgd))
> + goto error_with_snapshot;
> +
> + if (__pkvm_host_donate_hyp(hyp_virt_to_pfn(pgd), snap->pgd_pages))
> + goto error_with_snapshot;
> +
> + mc_page = snap->mc.head;
> + for (i = 0; i < snap->mc.nr_pages; i++) {
> + if (!PAGE_ALIGNED(mc_page))
> + goto error_with_memcache;
> +
> + if (__pkvm_host_donate_hyp(hyp_phys_to_pfn(mc_page), 1))
> + goto error_with_memcache;
> +
> + mc_page = *((phys_addr_t *)hyp_phys_to_virt(mc_page));
> + }
> +
> + used_pg = kern_hyp_va(snap->used_pages_hva);
> + if (!PAGE_ALIGNED(used_pg))
> + goto error_with_memcache;
> +
> + if (__pkvm_host_donate_hyp(hyp_virt_to_pfn(used_pg), snap->num_used_pages))
> + goto error_with_memcache;
> +
> + return snap;
> +error_with_memcache:
> + mc_page = snap->mc.head;
> + for (; i >= 0; i--) {
> + next_mc_page = *((phys_addr_t *)hyp_phys_to_virt(mc_page));
> + WARN_ON(__pkvm_hyp_donate_host(hyp_phys_to_pfn(mc_page), 1));
> + mc_page = next_mc_page;
> + }
> +
> + WARN_ON(__pkvm_hyp_donate_host(hyp_virt_to_pfn(pgd), snap->pgd_pages));
> +error_with_snapshot:
> + WARN_ON(__pkvm_hyp_donate_host(hyp_virt_to_pfn(snap), 1));
> + return NULL;
> +}
> +
> +static void pkvm_teardown_snapshot(struct kvm_pgtable_snapshot *snap)
> +{
> + size_t i;
> + phys_addr_t mc_page, next_mc_page;
> + u64 *used_pg = kern_hyp_va(snap->used_pages_hva);
> + void *pgd = kern_hyp_va(snap->pgd_hva);
> +
> + for (i = 0; i < snap->used_pages_indx; i++) {
> + mc_page = used_pg[i];
> + WARN_ON(__pkvm_hyp_donate_host(hyp_phys_to_pfn(mc_page), 1));
> + }
> +
> + WARN_ON(__pkvm_hyp_donate_host(hyp_virt_to_pfn(used_pg),
> + snap->num_used_pages));
> +
> + mc_page = snap->mc.head;
> + for (i = 0; i < snap->mc.nr_pages; i++) {
> + next_mc_page = *((phys_addr_t *)hyp_phys_to_virt(mc_page));
> + WARN_ON(__pkvm_hyp_donate_host(hyp_phys_to_pfn(mc_page), 1));
> + mc_page = next_mc_page;
> + }
> +
> + snap->pgtable.mm_ops = NULL;
> + WARN_ON(__pkvm_hyp_donate_host(hyp_virt_to_pfn(pgd), snap->pgd_pages));
> + WARN_ON(__pkvm_hyp_donate_host(hyp_virt_to_pfn(snap), 1));
> +}
> +
> +static int pkvm_host_stage2_snapshot(struct kvm_pgtable_snapshot *snap)
> +{
> + int ret;
> + void *pgd;
> + size_t required_pgd_len;
> + struct kvm_pgtable_mm_ops mm_ops = {0};
> + struct kvm_s2_mmu *mmu;
> + struct kvm_pgtable *to_pgt, *from_pgt;
> +
> + if (snap->used_pages_indx != 0)
> + return -EINVAL;
> +
> + from_pgt = &host_mmu.pgt;
> + mmu = &host_mmu.arch.mmu;
> + required_pgd_len = kvm_pgtable_stage2_pgd_size(mmu->vtcr);
> + if (snap->pgd_pages < (required_pgd_len >> PAGE_SHIFT))
> + return -ENOMEM;
> +
> + if (snap->mc.nr_pages < host_s2_pgtable_pages())
> + return -ENOMEM;
> +
> + to_pgt = &snap->pgtable;
> + pgd = kern_hyp_va(snap->pgd_hva);
> +
> + mm_ops.zalloc_page = snap_zalloc_page;
> + mm_ops.free_pages_exact = snap_free_pages_exact;
> + mm_ops.phys_to_virt = hyp_phys_to_virt;
> + mm_ops.virt_to_phys = hyp_virt_to_phys;
> + mm_ops.page_count = hyp_page_count;
> +
> + to_pgt->ia_bits = from_pgt->ia_bits;
> + to_pgt->start_level = from_pgt->start_level;
> + to_pgt->flags = from_pgt->flags;
> + to_pgt->mm_ops = &mm_ops;
> +
> + host_lock_component();
> +
> + to_pgt->pgd = pgd;
> + memcpy(to_pgt->pgd, from_pgt->pgd, required_pgd_len);
> + ret = kvm_pgtable_stage2_snapshot(to_pgt, &snap->mc);
> +
> + host_unlock_component();
> +
> + return ret;
> +}
> +
> +int __pkvm_host_stage2_snapshot(struct kvm_pgtable_snapshot *snap_hva)
> +{
> + int ret;
> + struct kvm_pgtable_snapshot *snap;
> + kvm_pteref_t pgd;
> +
> + snap = pkvm_setup_snapshot(snap_hva);
> + if (!snap)
> + return -EPERM;
> +
> + ret = pkvm_host_stage2_snapshot(snap);
> + if (!ret) {
> + pgd = snap->pgtable.pgd;
> + snap->pgtable.pgd = (kvm_pteref_t)__hyp_pa(pgd);
> + }
> + pkvm_teardown_snapshot(snap);
> + return ret;
> +}
> +#endif /* CONFIG_NVHE_EL2_DEBUG */
> +
> void reclaim_guest_pages(struct pkvm_hyp_vm *vm, struct kvm_hyp_memcache *mc)
> {
> void *addr;
> diff --git a/arch/arm64/kvm/hyp/pgtable.c b/arch/arm64/kvm/hyp/pgtable.c
> index 1966fdee7..82fef9620 100644
> --- a/arch/arm64/kvm/hyp/pgtable.c
> +++ b/arch/arm64/kvm/hyp/pgtable.c
> @@ -1598,3 +1598,46 @@ void kvm_pgtable_stage2_free_unlinked(struct kvm_pgtable_mm_ops *mm_ops, void *p
> WARN_ON(mm_ops->page_count(pgtable) != 1);
> mm_ops->put_page(pgtable);
> }
> +
> +#ifdef CONFIG_NVHE_EL2_DEBUG
> +static int snapshot_walker(const struct kvm_pgtable_visit_ctx *ctx,
> + enum kvm_pgtable_walk_flags visit)
> +{
> + struct kvm_pgtable_mm_ops *mm_ops = ctx->mm_ops;
> + void *copy_table, *original_addr;
> + kvm_pte_t new = ctx->old;
> +
> + if (!stage2_pte_is_counted(ctx->old))
> + return 0;
> +
> + if (kvm_pte_table(ctx->old, ctx->level)) {
> + copy_table = mm_ops->zalloc_page(ctx->arg);
> + if (!copy_table)
> + return -ENOMEM;
> +
> + original_addr = kvm_pte_follow(ctx->old, mm_ops);
> +
> + memcpy(copy_table, original_addr, PAGE_SIZE);
> + new = kvm_init_table_pte(copy_table, mm_ops);
> + }
> +
> + *ctx->ptep = new;
> +
> + return 0;
> +}
> +
> +int kvm_pgtable_stage2_snapshot(struct kvm_pgtable *to_pgt, void *mc)
> +{
> + struct kvm_pgtable_walker walker = {
> + .cb = snapshot_walker,
> + .flags = KVM_PGTABLE_WALK_LEAF |
> + KVM_PGTABLE_WALK_TABLE_PRE,
> + .arg = mc
> + };
> +
> + if (!to_pgt->pgd)
> + return -ENOMEM;
> +
> + return kvm_pgtable_walk(to_pgt, 0, BIT(to_pgt->ia_bits), &walker);
> +}
> +#endif /* CONFIG_NVHE_EL2_DEBUG */
> --
> 2.43.0.472.g3155946c3a-goog
>
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