[PATCH v4 03/25] KVM: arm64: Back the hypervisor 'struct hyp_page' array for all memory

Will Deacon
2022-10-17T11:54:06Z

From: Quentin Perret <qperret@google.com>

The EL2 'vmemmap' array in nVHE Protected mode is currently very sparse:
only memory pages owned by the hypervisor itself have a matching 'struct
hyp_page'. However, as the size of this struct has been reduced
significantly since its introduction, it appears that we can now afford
to back the vmemmap for all of memory.

Having an easily accessible 'struct hyp_page' for every physical page in
memory provides the hypervisor with a simple mechanism to store metadata
(e.g. a refcount) that wouldn't otherwise fit in the very limited number
of software bits available in the host stage-2 page-table entries. This
will be used in subsequent patches when pinning host memory pages for
use by the hypervisor at EL2.

Tested-by: Vincent Donnefort <vdonnefort@google.com>
Signed-off-by: Quentin Perret <qperret@google.com>
Signed-off-by: Will Deacon <will@kernel.org>
---
arch/arm64/include/asm/kvm_pkvm.h | 26 +++++++++++++++++++++++
arch/arm64/kvm/hyp/include/nvhe/mm.h | 14 +------------
arch/arm64/kvm/hyp/nvhe/mm.c | 31 ++++++++++++++++++++++++----
arch/arm64/kvm/hyp/nvhe/page_alloc.c | 4 +---
arch/arm64/kvm/hyp/nvhe/setup.c | 7 +++----
arch/arm64/kvm/pkvm.c | 18 ++--------------
6 files changed, 60 insertions(+), 40 deletions(-)

diff --git a/arch/arm64/include/asm/kvm_pkvm.h b/arch/arm64/include/asm/kvm_pkvm.h
index 9f4ad2a8df59..8f7b8a2314bb 100644
--- a/arch/arm64/include/asm/kvm_pkvm.h
+++ b/arch/arm64/include/asm/kvm_pkvm.h
@@ -14,6 +14,32 @@
extern struct memblock_region kvm_nvhe_sym(hyp_memory)[];
extern unsigned int kvm_nvhe_sym(hyp_memblock_nr);

+static inline unsigned long
+hyp_vmemmap_memblock_size(struct memblock_region *reg, size_t vmemmap_entry_size)
+{
+ unsigned long nr_pages = reg->size >> PAGE_SHIFT;
+ unsigned long start, end;
+
+ start = (reg->base >> PAGE_SHIFT) * vmemmap_entry_size;
+ end = start + nr_pages * vmemmap_entry_size;
+ start = ALIGN_DOWN(start, PAGE_SIZE);
+ end = ALIGN(end, PAGE_SIZE);
+
+ return end - start;
+}
+
+static inline unsigned long hyp_vmemmap_pages(size_t vmemmap_entry_size)
+{
+ unsigned long res = 0, i;
+
+ for (i = 0; i < kvm_nvhe_sym(hyp_memblock_nr); i++) {
+ res += hyp_vmemmap_memblock_size(&kvm_nvhe_sym(hyp_memory)[i],
+ vmemmap_entry_size);
+ }
+
+ return res >> PAGE_SHIFT;
+}
+
static inline unsigned long __hyp_pgtable_max_pages(unsigned long nr_pages)
{
unsigned long total = 0, i;
diff --git a/arch/arm64/kvm/hyp/include/nvhe/mm.h b/arch/arm64/kvm/hyp/include/nvhe/mm.h
index 42d8eb9bfe72..b2ee6d5df55b 100644
--- a/arch/arm64/kvm/hyp/include/nvhe/mm.h
+++ b/arch/arm64/kvm/hyp/include/nvhe/mm.h
@@ -15,7 +15,7 @@ extern hyp_spinlock_t pkvm_pgd_lock;

int hyp_create_idmap(u32 hyp_va_bits);
int hyp_map_vectors(void);
-int hyp_back_vmemmap(phys_addr_t phys, unsigned long size, phys_addr_t back);
+int hyp_back_vmemmap(phys_addr_t back);
int pkvm_cpu_set_vector(enum arm64_hyp_spectre_vector slot);
int pkvm_create_mappings(void *from, void *to, enum kvm_pgtable_prot prot);
int pkvm_create_mappings_locked(void *from, void *to, enum kvm_pgtable_prot prot);
@@ -24,16 +24,4 @@ int __pkvm_create_private_mapping(phys_addr_t phys, size_t size,
unsigned long *haddr);
int pkvm_alloc_private_va_range(size_t size, unsigned long *haddr);

-static inline void hyp_vmemmap_range(phys_addr_t phys, unsigned long size,
- unsigned long *start, unsigned long *end)
-{
- unsigned long nr_pages = size >> PAGE_SHIFT;
- struct hyp_page *p = hyp_phys_to_page(phys);
-
- *start = (unsigned long)p;
- *end = *start + nr_pages * sizeof(struct hyp_page);
- *start = ALIGN_DOWN(*start, PAGE_SIZE);
- *end = ALIGN(*end, PAGE_SIZE);
-}
-
#endif /* __KVM_HYP_MM_H */
diff --git a/arch/arm64/kvm/hyp/nvhe/mm.c b/arch/arm64/kvm/hyp/nvhe/mm.c
index 96193cb31a39..d3a3b47181de 100644
--- a/arch/arm64/kvm/hyp/nvhe/mm.c
+++ b/arch/arm64/kvm/hyp/nvhe/mm.c
@@ -129,13 +129,36 @@ int pkvm_create_mappings(void *from, void *to, enum kvm_pgtable_prot prot)
return ret;
}

-int hyp_back_vmemmap(phys_addr_t phys, unsigned long size, phys_addr_t back)
+int hyp_back_vmemmap(phys_addr_t back)
{
- unsigned long start, end;
+ unsigned long i, start, size, end = 0;
+ int ret;

- hyp_vmemmap_range(phys, size, &start, &end);
+ for (i = 0; i < hyp_memblock_nr; i++) {
+ start = hyp_memory[i].base;
+ start = ALIGN_DOWN((u64)hyp_phys_to_page(start), PAGE_SIZE);
+ /*
+ * The begining of the hyp_vmemmap region for the current
+ * memblock may already be backed by the page backing the end
+ * the previous region, so avoid mapping it twice.
+ */
+ start = max(start, end);
+
+ end = hyp_memory[i].base + hyp_memory[i].size;
+ end = PAGE_ALIGN((u64)hyp_phys_to_page(end));
+ if (start >= end)
+ continue;
+
+ size = end - start;
+ ret = __pkvm_create_mappings(start, size, back, PAGE_HYP);
+ if (ret)
+ return ret;
+
+ memset(hyp_phys_to_virt(back), 0, size);
+ back += size;
+ }

- return __pkvm_create_mappings(start, end - start, back, PAGE_HYP);
+ return 0;
}

static void *__hyp_bp_vect_base;
diff --git a/arch/arm64/kvm/hyp/nvhe/page_alloc.c b/arch/arm64/kvm/hyp/nvhe/page_alloc.c
index 0d15227aced8..7804da89e55d 100644
--- a/arch/arm64/kvm/hyp/nvhe/page_alloc.c
+++ b/arch/arm64/kvm/hyp/nvhe/page_alloc.c
@@ -235,10 +235,8 @@ int hyp_pool_init(struct hyp_pool *pool, u64 pfn, unsigned int nr_pages,

/* Init the vmemmap portion */
p = hyp_phys_to_page(phys);
- for (i = 0; i < nr_pages; i++) {
- p[i].order = 0;
+ for (i = 0; i < nr_pages; i++)
hyp_set_page_refcounted(&p[i]);
- }

/* Attach the unused pages to the buddy tree */
for (i = reserved_pages; i < nr_pages; i++)
diff --git a/arch/arm64/kvm/hyp/nvhe/setup.c b/arch/arm64/kvm/hyp/nvhe/setup.c
index e8d4ea2fcfa0..579eb4f73476 100644
--- a/arch/arm64/kvm/hyp/nvhe/setup.c
+++ b/arch/arm64/kvm/hyp/nvhe/setup.c
@@ -31,12 +31,11 @@ static struct hyp_pool hpool;

static int divide_memory_pool(void *virt, unsigned long size)
{
- unsigned long vstart, vend, nr_pages;
+ unsigned long nr_pages;

hyp_early_alloc_init(virt, size);

- hyp_vmemmap_range(__hyp_pa(virt), size, &vstart, &vend);
- nr_pages = (vend - vstart) >> PAGE_SHIFT;
+ nr_pages = hyp_vmemmap_pages(sizeof(struct hyp_page));
vmemmap_base = hyp_early_alloc_contig(nr_pages);
if (!vmemmap_base)
return -ENOMEM;
@@ -78,7 +77,7 @@ static int recreate_hyp_mappings(phys_addr_t phys, unsigned long size,
if (ret)
return ret;

- ret = hyp_back_vmemmap(phys, size, hyp_virt_to_phys(vmemmap_base));
+ ret = hyp_back_vmemmap(hyp_virt_to_phys(vmemmap_base));
if (ret)
return ret;

diff --git a/arch/arm64/kvm/pkvm.c b/arch/arm64/kvm/pkvm.c
index ebecb7c045f4..34229425b25d 100644
--- a/arch/arm64/kvm/pkvm.c
+++ b/arch/arm64/kvm/pkvm.c
@@ -53,7 +53,7 @@ static int __init register_memblock_regions(void)

void __init kvm_hyp_reserve(void)
{
- u64 nr_pages, prev, hyp_mem_pages = 0;
+ u64 hyp_mem_pages = 0;
int ret;

if (!is_hyp_mode_available() || is_kernel_in_hyp_mode())
@@ -71,21 +71,7 @@ void __init kvm_hyp_reserve(void)

hyp_mem_pages += hyp_s1_pgtable_pages();
hyp_mem_pages += host_s2_pgtable_pages();
-
- /*
- * The hyp_vmemmap needs to be backed by pages, but these pages
- * themselves need to be present in the vmemmap, so compute the number
- * of pages needed by looking for a fixed point.
- */
- nr_pages = 0;
- do {
- prev = nr_pages;
- nr_pages = hyp_mem_pages + prev;
- nr_pages = DIV_ROUND_UP(nr_pages * STRUCT_HYP_PAGE_SIZE,
- PAGE_SIZE);
- nr_pages += __hyp_pgtable_max_pages(nr_pages);
- } while (nr_pages != prev);
- hyp_mem_pages += nr_pages;
+ hyp_mem_pages += hyp_vmemmap_pages(STRUCT_HYP_PAGE_SIZE);

/*
* Try to allocate a PMD-aligned region to reduce TLB pressure once
--
2.38.0.413.g74048e4d9e-goog