[PATCH v3 12/15] KVM: arm64: Implement __pkvm_host_share_hyp() using do_share()

Quentin Perret
2021-12-01T17:11:22Z

From: Will Deacon <will@kernel.org>

__pkvm_host_share_hyp() shares memory between the host and the
hypervisor so implement it as an invocation of the new do_share()
mechanism.

Note that double-sharing is no longer permitted (as this allows us to
reduce the number of page-table walks significantly), but is thankfully
no longer relied upon by the host.

Signed-off-by: Will Deacon <will@kernel.org>
Signed-off-by: Quentin Perret <qperret@google.com>
---
arch/arm64/kvm/hyp/nvhe/mem_protect.c | 121 +++++++-------------------
1 file changed, 33 insertions(+), 88 deletions(-)

diff --git a/arch/arm64/kvm/hyp/nvhe/mem_protect.c b/arch/arm64/kvm/hyp/nvhe/mem_protect.c
index 74ca4043b08a..1282cbd6b9b3 100644
--- a/arch/arm64/kvm/hyp/nvhe/mem_protect.c
+++ b/arch/arm64/kvm/hyp/nvhe/mem_protect.c
@@ -370,94 +370,6 @@ static int host_stage2_idmap(u64 addr)
return ret;
}

-static inline bool check_prot(enum kvm_pgtable_prot prot,
- enum kvm_pgtable_prot required,
- enum kvm_pgtable_prot denied)
-{
- return (prot & (required | denied)) == required;
-}
-
-int __pkvm_host_share_hyp(u64 pfn)
-{
- phys_addr_t addr = hyp_pfn_to_phys(pfn);
- enum kvm_pgtable_prot prot, cur;
- void *virt = __hyp_va(addr);
- enum pkvm_page_state state;
- kvm_pte_t pte;
- int ret;
-
- if (!addr_is_memory(addr))
- return -EINVAL;
-
- host_lock_component();
- hyp_lock_component();
-
- ret = kvm_pgtable_get_leaf(&host_kvm.pgt, addr, &pte, NULL);
- if (ret)
- goto unlock;
- if (!pte)
- goto map_shared;
-
- /*
- * Check attributes in the host stage-2 PTE. We need the page to be:
- * - mapped RWX as we're sharing memory;
- * - not borrowed, as that implies absence of ownership.
- * Otherwise, we can't let it got through
- */
- cur = kvm_pgtable_stage2_pte_prot(pte);
- prot = pkvm_mkstate(0, PKVM_PAGE_SHARED_BORROWED);
- if (!check_prot(cur, PKVM_HOST_MEM_PROT, prot)) {
- ret = -EPERM;
- goto unlock;
- }
-
- state = pkvm_getstate(cur);
- if (state == PKVM_PAGE_OWNED)
- goto map_shared;
-
- /*
- * Tolerate double-sharing the same page, but this requires
- * cross-checking the hypervisor stage-1.
- */
- if (state != PKVM_PAGE_SHARED_OWNED) {
- ret = -EPERM;
- goto unlock;
- }
-
- ret = kvm_pgtable_get_leaf(&pkvm_pgtable, (u64)virt, &pte, NULL);
- if (ret)
- goto unlock;
-
- /*
- * If the page has been shared with the hypervisor, it must be
- * already mapped as SHARED_BORROWED in its stage-1.
- */
- cur = kvm_pgtable_hyp_pte_prot(pte);
- prot = pkvm_mkstate(PAGE_HYP, PKVM_PAGE_SHARED_BORROWED);
- if (!check_prot(cur, prot, ~prot))
- ret = -EPERM;
- goto unlock;
-
-map_shared:
- /*
- * If the page is not yet shared, adjust mappings in both page-tables
- * while both locks are held.
- */
- prot = pkvm_mkstate(PAGE_HYP, PKVM_PAGE_SHARED_BORROWED);
- ret = pkvm_create_mappings_locked(virt, virt + PAGE_SIZE, prot);
- BUG_ON(ret);
-
- prot = pkvm_mkstate(PKVM_HOST_MEM_PROT, PKVM_PAGE_SHARED_OWNED);
- ret = host_stage2_idmap_locked(addr, PAGE_SIZE, prot);
- BUG_ON(ret);
-
-unlock:
- hyp_unlock_component();
- host_unlock_component();
-
- return ret;
-}
-
void handle_host_mem_abort(struct kvm_cpu_context *host_ctxt)
{
struct kvm_vcpu_fault_info fault;
@@ -708,3 +620,36 @@ static int do_share(struct pkvm_mem_share *share)

return WARN_ON(__do_share(share));
}
+
+int __pkvm_host_share_hyp(u64 pfn)
+{
+ int ret;
+ u64 host_addr = hyp_pfn_to_phys(pfn);
+ u64 hyp_addr = (u64)__hyp_va(host_addr);
+ struct pkvm_mem_share share = {
+ .tx = {
+ .nr_pages = 1,
+ .initiator = {
+ .id = PKVM_ID_HOST,
+ .addr = host_addr,
+ .host = {
+ .completer_addr = hyp_addr,
+ },
+ },
+ .completer = {
+ .id = PKVM_ID_HYP,
+ },
+ },
+ .prot = PAGE_HYP,
+ };
+
+ host_lock_component();
+ hyp_lock_component();
+
+ ret = do_share(&share);
+
+ hyp_unlock_component();
+ host_unlock_component();
+
+ return ret;
+}
--
2.34.0.rc2.393.gf8c9666880-goog