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Subject[RFC PATCH V2 09/11] KVM: VMX: Update the EPT leaf entry indicated with the SPP enable bit.
Date
If the sub-page write permission VM-execution control is set,
treatment of write accesses to guest-physical accesses
depends on the state of the accumulated write-access bit (position 1)
and sub-page permission bit (position 61) in the EPT leaf paging-structure.

Software will update the EPT leaf entry sub-page permission bit while
kvm_set_subpage. If the EPT write-access bit set to 0 and the SPP bit
set to 1 in the leaf EPT paging-structure entry that maps a 4KB page,
then the hardware will look up a VMM-managed Sub-Page Permission Table
(SPPT), which will also be prepared by setup kvm_set_subpage.

Signed-off-by: Zhang Yi <yi.z.zhang@linux.intel.com>
---
arch/x86/kvm/mmu.c | 100 +++++++++++++++++++++++++++++++++++++++++++++++++++++
1 file changed, 100 insertions(+)

diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
index b1773c6..d512125 100644
--- a/arch/x86/kvm/mmu.c
+++ b/arch/x86/kvm/mmu.c
@@ -1668,6 +1668,87 @@ int kvm_arch_write_log_dirty(struct kvm_vcpu *vcpu)
return 0;
}

+static bool __rmap_open_subpage_bit(struct kvm *kvm,
+ struct kvm_rmap_head *rmap_head)
+{
+ struct rmap_iterator iter;
+ bool flush = false;
+ u64 *sptep;
+ u64 spte;
+
+ for_each_rmap_spte(rmap_head, &iter, sptep) {
+ /*
+ * SPP works only when the page is unwritable
+ * and SPP bit is set
+ */
+ flush |= spte_write_protect(sptep, false);
+ spte = *sptep | PT_SPP_MASK;
+ flush |= mmu_spte_update(sptep, spte);
+ }
+
+ return flush;
+}
+
+static int kvm_mmu_open_subpage_write_protect(struct kvm *kvm,
+ struct kvm_memory_slot *slot,
+ gfn_t gfn)
+{
+ struct kvm_rmap_head *rmap_head;
+ bool flush = false;
+
+ /*
+ * we only support spp in a normal 4K level 1 page frame
+ * If it a huge page, we drop it.
+ */
+ rmap_head = __gfn_to_rmap(gfn, PT_PAGE_TABLE_LEVEL, slot);
+
+ if (!rmap_head->val)
+ return -EFAULT;
+
+ flush |= __rmap_open_subpage_bit(kvm, rmap_head);
+
+ if (flush)
+ kvm_flush_remote_tlbs(kvm);
+
+ return 0;
+}
+
+static bool __rmap_clear_subpage_bit(struct kvm *kvm,
+ struct kvm_rmap_head *rmap_head)
+{
+ struct rmap_iterator iter;
+ bool flush = false;
+ u64 *sptep;
+ u64 spte;
+
+ for_each_rmap_spte(rmap_head, &iter, sptep) {
+ spte = (*sptep & ~PT_SPP_MASK) | PT_WRITABLE_MASK;
+ flush |= mmu_spte_update(sptep, spte);
+ }
+
+ return flush;
+}
+
+static int kvm_mmu_clear_subpage_write_protect(struct kvm *kvm,
+ struct kvm_memory_slot *slot,
+ gfn_t gfn)
+{
+ struct kvm_rmap_head *rmap_head;
+ bool flush = false;
+
+ rmap_head = __gfn_to_rmap(gfn, PT_PAGE_TABLE_LEVEL, slot);
+
+ if (!rmap_head->val)
+ return -EFAULT;
+
+ flush |= __rmap_clear_subpage_bit(kvm, rmap_head);
+
+ if (flush)
+ kvm_flush_remote_tlbs(kvm);
+
+ return 0;
+}
+
bool kvm_mmu_slot_gfn_write_protect(struct kvm *kvm,
struct kvm_memory_slot *slot, u64 gfn)
{
@@ -4175,12 +4256,31 @@ int kvm_mmu_set_subpages(struct kvm *kvm, struct kvm_subpage *spp_info)
int npages = spp_info->npages;
struct kvm_memory_slot *slot;
u32 *wp_map;
+ int ret;
int i;

for (i = 0; i < npages; i++, gfn++) {
slot = gfn_to_memslot(kvm, gfn);
if (!slot)
return -EFAULT;
+
+ /*
+ * open SPP bit in EPT leaf entry to write protect the
+ * sub-pages in corresponding page
+ */
+ if (access != (u32)((1ULL << 32) - 1))
+ ret = kvm_mmu_open_subpage_write_protect(kvm,
+ slot, gfn);
+ else
+ ret = kvm_mmu_clear_subpage_write_protect(kvm,
+ slot, gfn);
+
+ if (ret) {
+ pr_info("SPP ,didn't get the gfn:%llx from EPT leaf level1\n"
+ "Current we didn't support huge page on SPP\n"
+ "Please try to disable the huge page\n", gfn);
+ return -EFAULT;
+ }
wp_map = gfn_to_subpage_wp_info(slot, gfn);
*wp_map = access;
}
--
2.7.4
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