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[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] [xen staging] xen/riscv: add support of page lookup by GFN
commit 27fe81330553ac5edab4ca8ab5435cb0a36e5b1f
Author: Oleksii Kurochko <oleksii.kurochko@xxxxxxxxx>
AuthorDate: Mon Jan 12 13:06:14 2026 +0100
Commit: Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Mon Jan 12 13:06:14 2026 +0100
xen/riscv: add support of page lookup by GFN
Introduce helper functions for safely querying the P2M (physical-to-machine)
mapping:
- add p2m_read_lock(), p2m_read_unlock(), and p2m_is_locked() for managing
P2M lock state.
- Implement p2m_get_entry() to retrieve mapping details for a given GFN,
including MFN, page order, and validity.
- Introduce p2m_get_page_from_gfn() to convert a GFN into a page_info
pointer, acquiring a reference to the page if valid.
- Introduce get_page().
Implementations are based on Arm's functions with some minor modifications:
- p2m_get_entry():
- Reverse traversal of page tables, as RISC-V uses the opposite level
numbering compared to Arm.
- Removed the return of p2m_access_t from p2m_get_entry() since
mem_access_settings is not introduced for RISC-V.
- Updated BUILD_BUG_ON() to check using the level 0 mask, which
corresponds
to Arm's THIRD_MASK.
- Replaced open-coded bit shifts with the BIT() macro.
Signed-off-by: Oleksii Kurochko <oleksii.kurochko@xxxxxxxxx>
Acked-by: Jan Beulich <jbeulich@xxxxxxxx>
---
xen/arch/riscv/include/asm/p2m.h | 21 +++++
xen/arch/riscv/mm.c | 13 +++
xen/arch/riscv/p2m.c | 185 +++++++++++++++++++++++++++++++++++++++
3 files changed, 219 insertions(+)
diff --git a/xen/arch/riscv/include/asm/p2m.h b/xen/arch/riscv/include/asm/p2m.h
index b48693a2b4..f63b5dec99 100644
--- a/xen/arch/riscv/include/asm/p2m.h
+++ b/xen/arch/riscv/include/asm/p2m.h
@@ -41,6 +41,9 @@
#define P2M_GFN_LEVEL_SHIFT(lvl) (P2M_LEVEL_ORDER(lvl) + PAGE_SHIFT)
+#define P2M_LEVEL_MASK(p2m, lvl) \
+ (P2M_TABLE_OFFSET(p2m, lvl) << P2M_GFN_LEVEL_SHIFT(lvl))
+
#define paddr_bits PADDR_BITS
/* Get host p2m table */
@@ -234,6 +237,24 @@ static inline bool p2m_is_write_locked(struct p2m_domain
*p2m)
unsigned long construct_hgatp(const struct p2m_domain *p2m, uint16_t vmid);
+static inline void p2m_read_lock(struct p2m_domain *p2m)
+{
+ read_lock(&p2m->lock);
+}
+
+static inline void p2m_read_unlock(struct p2m_domain *p2m)
+{
+ read_unlock(&p2m->lock);
+}
+
+static inline bool p2m_is_locked(const struct p2m_domain *p2m)
+{
+ return rw_is_locked(&p2m->lock);
+}
+
+struct page_info *p2m_get_page_from_gfn(struct p2m_domain *p2m, gfn_t gfn,
+ p2m_type_t *t);
+
#endif /* ASM__RISCV__P2M_H */
/*
diff --git a/xen/arch/riscv/mm.c b/xen/arch/riscv/mm.c
index e25f995b72..e9ce182d06 100644
--- a/xen/arch/riscv/mm.c
+++ b/xen/arch/riscv/mm.c
@@ -673,3 +673,16 @@ struct domain *page_get_owner_and_reference(struct
page_info *page)
return owner;
}
+
+bool get_page(struct page_info *page, const struct domain *domain)
+{
+ const struct domain *owner = page_get_owner_and_reference(page);
+
+ if ( likely(owner == domain) )
+ return true;
+
+ if ( owner != NULL )
+ put_page(page);
+
+ return false;
+}
diff --git a/xen/arch/riscv/p2m.c b/xen/arch/riscv/p2m.c
index 8d572f838f..c6de785e4c 100644
--- a/xen/arch/riscv/p2m.c
+++ b/xen/arch/riscv/p2m.c
@@ -1057,3 +1057,188 @@ int map_regions_p2mt(struct domain *d,
return rc;
}
+
+/*
+ * p2m_get_entry() should always return the correct order value, even if an
+ * entry is not present (i.e. the GFN is outside the range):
+ * [p2m->lowest_mapped_gfn, p2m->max_mapped_gfn] (1)
+ *
+ * This ensures that callers of p2m_get_entry() can determine what range of
+ * address space would be altered by a corresponding p2m_set_entry().
+ * Also, it would help to avoid costly page walks for GFNs outside range (1).
+ *
+ * Therefore, this function returns true for GFNs outside range (1), and in
+ * that case the corresponding level is returned via the level_out argument.
+ * Otherwise, it returns false and p2m_get_entry() performs a page walk to
+ * find the proper entry.
+ */
+static bool check_outside_boundary(const struct p2m_domain *p2m, gfn_t gfn,
+ gfn_t boundary, bool is_lower,
+ unsigned int *level_out)
+{
+ unsigned int level = P2M_MAX_ROOT_LEVEL + 1;
+ bool ret = false;
+
+ ASSERT(p2m);
+
+ if ( is_lower ? gfn_x(gfn) < gfn_x(boundary)
+ : gfn_x(gfn) > gfn_x(boundary) )
+ {
+ for ( level = P2M_ROOT_LEVEL(p2m) ; level; level-- )
+ {
+ unsigned long mask = BIT(P2M_GFN_LEVEL_SHIFT(level), UL) - 1;
+
+ if ( is_lower ? (gfn_x(gfn) | mask) < gfn_x(boundary)
+ : (gfn_x(gfn) & ~mask) > gfn_x(boundary) )
+ break;
+ }
+
+ ret = true;
+ }
+
+ if ( level_out )
+ *level_out = level;
+
+ return ret;
+}
+
+/*
+ * Get the details of a given gfn.
+ *
+ * If the entry is present, the associated MFN, the p2m type of the mapping,
+ * and the page order of the mapping in the page table (i.e., it could be a
+ * superpage) will be returned.
+ *
+ * If the entry is not present, INVALID_MFN will be returned, page_order will
+ * be set according to the order of the invalid range, and the type will be
+ * p2m_invalid.
+ */
+static mfn_t p2m_get_entry(struct p2m_domain *p2m, gfn_t gfn,
+ p2m_type_t *t,
+ unsigned int *page_order)
+{
+ unsigned int level = P2M_ROOT_LEVEL(p2m);
+ unsigned int gfn_limit_bits =
+ P2M_LEVEL_ORDER(level + 1) + P2M_ROOT_EXTRA_BITS(p2m, level);
+ pte_t entry, *table;
+ int rc;
+ mfn_t mfn = INVALID_MFN;
+
+ P2M_BUILD_LEVEL_OFFSETS(p2m, offsets, gfn_to_gaddr(gfn));
+
+ ASSERT(p2m_is_locked(p2m));
+
+ *t = p2m_invalid;
+
+ if ( gfn_x(gfn) > (BIT(gfn_limit_bits, UL) - 1) )
+ {
+ if ( page_order )
+ *page_order = gfn_limit_bits;
+
+ return mfn;
+ }
+
+ if ( check_outside_boundary(p2m, gfn, p2m->lowest_mapped_gfn, true,
+ &level) )
+ goto out;
+
+ if ( check_outside_boundary(p2m, gfn, p2m->max_mapped_gfn, false, &level) )
+ goto out;
+
+ table = p2m_get_root_pointer(p2m, gfn);
+
+ /*
+ * The table should always be non-NULL because the gfn is below
+ * p2m->max_mapped_gfn and the root table pages are always present.
+ */
+ if ( !table )
+ {
+ ASSERT_UNREACHABLE();
+ goto out;
+ }
+
+ for ( level = P2M_ROOT_LEVEL(p2m); level; level-- )
+ {
+ rc = p2m_next_level(p2m, false, level, &table, offsets[level]);
+ if ( rc == P2M_TABLE_MAP_NONE )
+ goto out_unmap;
+
+ if ( rc != P2M_TABLE_NORMAL )
+ break;
+ }
+
+ entry = table[offsets[level]];
+
+ if ( pte_is_valid(entry) )
+ {
+ *t = p2m_get_type(entry);
+
+ mfn = pte_get_mfn(entry);
+
+ ASSERT(!(mfn_x(mfn) & (BIT(P2M_LEVEL_ORDER(level), UL) - 1)));
+
+ /*
+ * The entry may point to a superpage. Find the MFN associated
+ * to the GFN.
+ */
+ mfn = mfn_add(mfn,
+ gfn_x(gfn) & (BIT(P2M_LEVEL_ORDER(level), UL) - 1));
+ }
+
+ out_unmap:
+ unmap_domain_page(table);
+
+ out:
+ if ( page_order )
+ *page_order = P2M_LEVEL_ORDER(level);
+
+ return mfn;
+}
+
+struct page_info *p2m_get_page_from_gfn(struct p2m_domain *p2m, gfn_t gfn,
+ p2m_type_t *t)
+{
+ struct page_info *page;
+ p2m_type_t p2mt;
+ mfn_t mfn;
+
+ p2m_read_lock(p2m);
+ mfn = p2m_get_entry(p2m, gfn, &p2mt, NULL);
+
+ if ( t )
+ *t = p2mt;
+
+ if ( !mfn_valid(mfn) )
+ {
+ p2m_read_unlock(p2m);
+ return NULL;
+ }
+
+ page = mfn_to_page(mfn);
+
+ /*
+ * get_page won't work on foreign mapping because the page doesn't
+ * belong to the current domain.
+ */
+ if ( unlikely(p2m_is_foreign(p2mt)) )
+ {
+ const struct domain *fdom = page_get_owner_and_reference(page);
+
+ p2m_read_unlock(p2m);
+
+ if ( fdom )
+ {
+ if ( likely(fdom != p2m->domain) )
+ return page;
+
+ ASSERT_UNREACHABLE();
+ put_page(page);
+ }
+
+ return NULL;
+ }
+
+ p2m_read_unlock(p2m);
+
+ return get_page(page, p2m->domain) ? page : NULL;
+}
--
generated by git-patchbot for /home/xen/git/xen.git#staging
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