On 8/7/2025 5:46 PM, Yan Zhao wrote:
From: "Kirill A. Shutemov" <kirill.shutemov@xxxxxxxxxxxxxxx>
Preallocate a page to be used in the split_external_spt() path.
Not just "a" page.
Kernel needs one PAMT page pair for external_spt and one that provided
directly to the TDH.MEM.PAGE.DEMOTE SEAMCALL.
Signed-off-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
Co-developed-by: Yan Zhao <yan.y.zhao@xxxxxxxxx>
Signed-off-by: Yan Zhao <yan.y.zhao@xxxxxxxxx>
---
RFC v2:
- Pulled from
git://git.kernel.org/pub/scm/linux/kernel/git/kas/linux.git tdx/dpamt-huge.
- Implemented the flow of topup pamt_page_cache in
tdp_mmu_split_huge_pages_root() (Yan)
---
arch/x86/include/asm/kvm_host.h | 2 ++
arch/x86/kvm/mmu/mmu.c | 1 +
arch/x86/kvm/mmu/tdp_mmu.c | 51 +++++++++++++++++++++++++++++++++
3 files changed, 54 insertions(+)
diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index 6b6c46c27390..508b133df903 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -1591,6 +1591,8 @@ struct kvm_arch {
#define SPLIT_DESC_CACHE_MIN_NR_OBJECTS (SPTE_ENT_PER_PAGE + 1)
struct kvm_mmu_memory_cache split_desc_cache;
+ struct kvm_mmu_memory_cache pamt_page_cache;
+
gfn_t gfn_direct_bits;
/*
diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
index f23d8fc59323..e581cee37f64 100644
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -6848,6 +6848,7 @@ static void mmu_free_vm_memory_caches(struct kvm *kvm)
kvm_mmu_free_memory_cache(&kvm->arch.split_desc_cache);
kvm_mmu_free_memory_cache(&kvm->arch.split_page_header_cache);
kvm_mmu_free_memory_cache(&kvm->arch.split_shadow_page_cache);
+ kvm_mmu_free_memory_cache(&kvm->arch.pamt_page_cache);
}
void kvm_mmu_uninit_vm(struct kvm *kvm)
diff --git a/arch/x86/kvm/mmu/tdp_mmu.c b/arch/x86/kvm/mmu/tdp_mmu.c
index eb758aaa4374..064c4e823658 100644
--- a/arch/x86/kvm/mmu/tdp_mmu.c
+++ b/arch/x86/kvm/mmu/tdp_mmu.c
@@ -1584,6 +1584,27 @@ static bool iter_cross_boundary(struct tdp_iter *iter, gfn_t start, gfn_t end)
(iter->gfn + KVM_PAGES_PER_HPAGE(iter->level)) <= end);
}
+static bool need_topup_mirror_caches(struct kvm *kvm)
+{
+ int nr = tdx_nr_pamt_pages() * 2;
+
+ return kvm_mmu_memory_cache_nr_free_objects(&kvm->arch.pamt_page_cache) < nr;
+}
+
+static int topup_mirror_caches(struct kvm *kvm)
+{
+ int r, nr;
+
+ /* One for external_spt, one for TDH.MEM.PAGE.DEMOTE */
The comment is a bit confusing.
IIUC, external_spt is also for TDH.MEM.PAGE.DEMOTE.
and it's "one pair" for PAMT pages.
+ nr = tdx_nr_pamt_pages() * 2;
+
+ r = kvm_mmu_topup_memory_cache(&kvm->arch.pamt_page_cache, nr);
+ if (r)
+ return r;
+
+ return 0;
This could be simplified:
diff --git a/arch/x86/kvm/mmu/tdp_mmu.c b/arch/x86/kvm/mmu/tdp_mmu.c
index 064c4e823658..35d052aa408c 100644
--- a/arch/x86/kvm/mmu/tdp_mmu.c
+++ b/arch/x86/kvm/mmu/tdp_mmu.c
@@ -1593,16 +1593,12 @@ static bool need_topup_mirror_caches(struct kvm *kvm)
static int topup_mirror_caches(struct kvm *kvm)
{
- int r, nr;
+ int nr;
/* One for external_spt, one for TDH.MEM.PAGE.DEMOTE */
nr = tdx_nr_pamt_pages() * 2;
- r = kvm_mmu_topup_memory_cache(&kvm->arch.pamt_page_cache, nr);
- if (r)
- return r;
-
- return 0;
+ return kvm_mmu_topup_memory_cache(&kvm->arch.pamt_page_cache, nr);
}
+}
+
static int tdp_mmu_split_huge_pages_root(struct kvm *kvm,
struct kvm_mmu_page *root,
gfn_t start, gfn_t end,
@@ -1656,6 +1677,36 @@ static int tdp_mmu_split_huge_pages_root(struct kvm *kvm,
continue;
}
+ if (is_mirror_sp(root) && need_topup_mirror_caches(kvm)) {
+ int r;
+
+ rcu_read_unlock();
+
+ if (shared)
+ read_unlock(&kvm->mmu_lock);
+ else
+ write_unlock(&kvm->mmu_lock);
+
+ r = topup_mirror_caches(kvm);
+
+ if (shared)
+ read_lock(&kvm->mmu_lock);
+ else
+ write_lock(&kvm->mmu_lock);
+
+ if (r) {
+ trace_kvm_mmu_split_huge_page(iter.gfn,
+ iter.old_spte,
+ iter.level, r);
+ return r;
+ }
+
+ rcu_read_lock();
+
+ iter.yielded = true;
+ continue;
+ }
+
tdp_mmu_init_child_sp(sp, &iter);
if (tdp_mmu_split_huge_page(kvm, &iter, sp, shared))
