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Message-ID: <20251127165137780QbUOVPKPAfWSGAFl5qtRy@zte.com.cn>
Date: Thu, 27 Nov 2025 16:51:37 +0800 (CST)
From: <liu.xuemei1@....com.cn>
To: <atish.patra@...ux.dev>, <alex@...ti.fr>, <anup@...infault.org>
Cc: <pjw@...nel.org>, <palmer@...belt.com>, <aou@...s.berkeley.edu>,
<kvm@...r.kernel.org>, <kvm-riscv@...ts.infradead.org>,
<inux-riscv@...ts.infradead.org>, <linux-kernel@...r.kernel.org>
Subject: [PATCH v4] RISC-V: KVM: Transparent huge page support
From: Jessica Liu <liu.xuemei1@....com.cn>
Use block mapping if backed by a THP, as implemented in architectures
like ARM and x86_64.
Signed-off-by: Jessica Liu <liu.xuemei1@....com.cn>
---
Changes in v4:
- Substituted kvm_riscv_gstage_get_mapping_size with get_hva_mapping_size
arch/riscv/kvm/mmu.c | 140 ++++++++++++++++++++++++++++++++++++++++
arch/riscv/mm/pgtable.c | 2 +
2 files changed, 142 insertions(+)
diff --git a/arch/riscv/kvm/mmu.c b/arch/riscv/kvm/mmu.c
index 58f5f3536ffd..38816c5895fe 100644
--- a/arch/riscv/kvm/mmu.c
+++ b/arch/riscv/kvm/mmu.c
@@ -302,6 +302,142 @@ bool kvm_test_age_gfn(struct kvm *kvm, struct kvm_gfn_range *range)
return pte_young(ptep_get(ptep));
}
+static bool fault_supports_gstage_huge_mapping(struct kvm_memory_slot *memslot,
+ unsigned long hva)
+{
+ hva_t uaddr_start, uaddr_end;
+ gpa_t gpa_start;
+ size_t size;
+
+ size = memslot->npages * PAGE_SIZE;
+ uaddr_start = memslot->userspace_addr;
+ uaddr_end = uaddr_start + size;
+
+ gpa_start = memslot->base_gfn << PAGE_SHIFT;
+
+ /*
+ * Pages belonging to memslots that don't have the same alignment
+ * within a PMD for userspace and GPA cannot be mapped with g-stage
+ * PMD entries, because we'll end up mapping the wrong pages.
+ *
+ * Consider a layout like the following:
+ *
+ * memslot->userspace_addr:
+ * +-----+--------------------+--------------------+---+
+ * |abcde|fgh vs-stage block | vs-stage block tv|xyz|
+ * +-----+--------------------+--------------------+---+
+ *
+ * memslot->base_gfn << PAGE_SHIFT:
+ * +---+--------------------+--------------------+-----+
+ * |abc|def g-stage block | g-stage block |tvxyz|
+ * +---+--------------------+--------------------+-----+
+ *
+ * If we create those g-stage blocks, we'll end up with this incorrect
+ * mapping:
+ * d -> f
+ * e -> g
+ * f -> h
+ */
+ if ((gpa_start & (PMD_SIZE - 1)) != (uaddr_start & (PMD_SIZE - 1)))
+ return false;
+
+ /*
+ * Next, let's make sure we're not trying to map anything not covered
+ * by the memslot. This means we have to prohibit block size mappings
+ * for the beginning and end of a non-block aligned and non-block sized
+ * memory slot (illustrated by the head and tail parts of the
+ * userspace view above containing pages 'abcde' and 'xyz',
+ * respectively).
+ *
+ * Note that it doesn't matter if we do the check using the
+ * userspace_addr or the base_gfn, as both are equally aligned (per
+ * the check above) and equally sized.
+ */
+ return (hva >= ALIGN(uaddr_start, PMD_SIZE)) && (hva < ALIGN_DOWN(uaddr_end, PMD_SIZE));
+}
+
+static int get_hva_mapping_size(struct kvm *kvm,
+ unsigned long hva)
+{
+ int size = PAGE_SIZE;
+ unsigned long flags;
+ pgd_t pgd;
+ p4d_t p4d;
+ pud_t pud;
+ pmd_t pmd;
+
+ /*
+ * Disable IRQs to prevent concurrent tear down of host page tables,
+ * e.g. if the primary MMU promotes a P*D to a huge page and then frees
+ * the original page table.
+ */
+ local_irq_save(flags);
+
+ /*
+ * Read each entry once. As above, a non-leaf entry can be promoted to
+ * a huge page _during_ this walk. Re-reading the entry could send the
+ * walk into the weeks, e.g. p*d_leaf() returns false (sees the old
+ * value) and then p*d_offset() walks into the target huge page instead
+ * of the old page table (sees the new value).
+ */
+ pgd = pgdp_get(pgd_offset(kvm->mm, hva));
+ if (pgd_none(pgd))
+ goto out;
+
+ p4d = p4dp_get(p4d_offset(&pgd, hva));
+ if (p4d_none(p4d) || !p4d_present(p4d))
+ goto out;
+
+ pud = pudp_get(pud_offset(&p4d, hva));
+ if (pud_none(pud) || !pud_present(pud))
+ goto out;
+
+ if (pud_leaf(pud)) {
+ size = PUD_SIZE;
+ goto out;
+ }
+
+ pmd = pmdp_get(pmd_offset(&pud, hva));
+ if (pmd_none(pmd) || !pmd_present(pmd))
+ goto out;
+
+ if (pmd_leaf(pmd))
+ size = PMD_SIZE;
+
+out:
+ local_irq_restore(flags);
+ return size;
+}
+
+static unsigned long transparent_hugepage_adjust(struct kvm *kvm,
+ struct kvm_memory_slot *memslot,
+ unsigned long hva,
+ kvm_pfn_t *hfnp, gpa_t *gpa)
+{
+ kvm_pfn_t hfn = *hfnp;
+
+ /*
+ * Make sure the adjustment is done only for THP pages. Also make
+ * sure that the HVA and GPA are sufficiently aligned and that the
+ * block map is contained within the memslot.
+ */
+ if (fault_supports_gstage_huge_mapping(memslot, hva)) {
+ int sz;
+
+ sz = get_hva_mapping_size(kvm, hva);
+ if (sz < PMD_SIZE)
+ return sz;
+
+ *gpa &= PMD_MASK;
+ hfn &= ~(PTRS_PER_PMD - 1);
+ *hfnp = hfn;
+
+ return PMD_SIZE;
+ }
+
+ return PAGE_SIZE;
+}
+
int kvm_riscv_mmu_map(struct kvm_vcpu *vcpu, struct kvm_memory_slot *memslot,
gpa_t gpa, unsigned long hva, bool is_write,
struct kvm_gstage_mapping *out_map)
@@ -395,6 +531,10 @@ int kvm_riscv_mmu_map(struct kvm_vcpu *vcpu, struct kvm_memory_slot *memslot,
if (mmu_invalidate_retry(kvm, mmu_seq))
goto out_unlock;
+ /* check if we are backed by a THP and thus use block mapping if possible */
+ if (vma_pagesize == PAGE_SIZE)
+ vma_pagesize = transparent_hugepage_adjust(kvm, memslot, hva, &hfn, &gpa);
+
if (writable) {
mark_page_dirty_in_slot(kvm, memslot, gfn);
ret = kvm_riscv_gstage_map_page(&gstage, pcache, gpa, hfn << PAGE_SHIFT,
diff --git a/arch/riscv/mm/pgtable.c b/arch/riscv/mm/pgtable.c
index 8b6c0a112a8d..fe776f03cc12 100644
--- a/arch/riscv/mm/pgtable.c
+++ b/arch/riscv/mm/pgtable.c
@@ -49,6 +49,7 @@ pud_t *pud_offset(p4d_t *p4d, unsigned long address)
return (pud_t *)p4d;
}
+EXPORT_SYMBOL_GPL(pud_offset);
p4d_t *p4d_offset(pgd_t *pgd, unsigned long address)
{
@@ -57,6 +58,7 @@ p4d_t *p4d_offset(pgd_t *pgd, unsigned long address)
return (p4d_t *)pgd;
}
+EXPORT_SYMBOL_GPL(p4d_offset);
#endif
#ifdef CONFIG_HAVE_ARCH_HUGE_VMAP
--
2.27.0
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