[RFC 15/16] KVM: Handle protected memory in __kvm_map_gfn()/__kvm_unmap_gfn()

Kirill A. Shutemov
2020-05-22T12:53:09Z

We cannot access protected pages directly. Use ioremap() to
create a temporary mapping of the page. The mapping is destroyed
on __kvm_unmap_gfn().

The new interface gfn_to_pfn_memslot_protected() is used to detect if
the page is protected.

ioremap_cache_force() is a hack to bypass IORES_MAP_SYSTEM_RAM check in
the x86 ioremap code. We need a better solution.

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
---
arch/x86/include/asm/io.h | 2 ++
arch/x86/include/asm/pgtable_types.h | 1 +
arch/x86/mm/ioremap.c | 16 +++++++++++++---
include/linux/kvm_host.h | 1 +
virt/kvm/kvm_main.c | 14 +++++++++++---
5 files changed, 28 insertions(+), 6 deletions(-)

diff --git a/arch/x86/include/asm/io.h b/arch/x86/include/asm/io.h
index c58d52fd7bf2..a3e1bfad1026 100644
--- a/arch/x86/include/asm/io.h
+++ b/arch/x86/include/asm/io.h
@@ -184,6 +184,8 @@ extern void __iomem *ioremap_uc(resource_size_t offset, unsigned long size);
#define ioremap_uc ioremap_uc
extern void __iomem *ioremap_cache(resource_size_t offset, unsigned long size);
#define ioremap_cache ioremap_cache
+extern void __iomem *ioremap_cache_force(resource_size_t offset, unsigned long size);
+#define ioremap_cache_force ioremap_cache_force
extern void __iomem *ioremap_prot(resource_size_t offset, unsigned long size, unsigned long prot_val);
#define ioremap_prot ioremap_prot
extern void __iomem *ioremap_encrypted(resource_size_t phys_addr, unsigned long size);
diff --git a/arch/x86/include/asm/pgtable_types.h b/arch/x86/include/asm/pgtable_types.h
index b6606fe6cfdf..66cc22abda7b 100644
--- a/arch/x86/include/asm/pgtable_types.h
+++ b/arch/x86/include/asm/pgtable_types.h
@@ -147,6 +147,7 @@ enum page_cache_mode {
_PAGE_CACHE_MODE_UC = 3,
_PAGE_CACHE_MODE_WT = 4,
_PAGE_CACHE_MODE_WP = 5,
+ _PAGE_CACHE_MODE_WB_FORCE = 6,

_PAGE_CACHE_MODE_NUM = 8
};
diff --git a/arch/x86/mm/ioremap.c b/arch/x86/mm/ioremap.c
index 18c637c0dc6f..e48fc0e130b2 100644
--- a/arch/x86/mm/ioremap.c
+++ b/arch/x86/mm/ioremap.c
@@ -202,9 +202,12 @@ __ioremap_caller(resource_size_t phys_addr, unsigned long size,
__ioremap_check_mem(phys_addr, size, &io_desc);

/*
- * Don't allow anybody to remap normal RAM that we're using..
+ * Don't allow anybody to remap normal RAM that we're using, unless
+ * _PAGE_CACHE_MODE_WB_FORCE is used.
*/
- if (io_desc.flags & IORES_MAP_SYSTEM_RAM) {
+ if (pcm == _PAGE_CACHE_MODE_WB_FORCE) {
+ pcm = _PAGE_CACHE_MODE_WB;
+ } else if (io_desc.flags & IORES_MAP_SYSTEM_RAM) {
WARN_ONCE(1, "ioremap on RAM at %pa - %pa\n",
&phys_addr, &last_addr);
return NULL;
@@ -419,6 +422,13 @@ void __iomem *ioremap_cache(resource_size_t phys_addr, unsigned long size)
}
EXPORT_SYMBOL(ioremap_cache);

+void __iomem *ioremap_cache_force(resource_size_t phys_addr, unsigned long size)
+{
+ return __ioremap_caller(phys_addr, size, _PAGE_CACHE_MODE_WB_FORCE,
+ __builtin_return_address(0), false);
+}
+EXPORT_SYMBOL(ioremap_cache_force);
+
void __iomem *ioremap_prot(resource_size_t phys_addr, unsigned long size,
unsigned long prot_val)
{
@@ -467,7 +477,7 @@ void iounmap(volatile void __iomem *addr)
p = find_vm_area((void __force *)addr);

if (!p) {
- printk(KERN_ERR "iounmap: bad address %p\n", addr);
+ printk(KERN_ERR "iounmap: bad address %px\n", addr);
dump_stack();
return;
}
diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index eca18ef9b1f4..b6944f88033d 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -237,6 +237,7 @@ struct kvm_host_map {
void *hva;
kvm_pfn_t pfn;
kvm_pfn_t gfn;
+ bool protected;
};

/*
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 8bcf3201304a..71aac117357f 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -2091,6 +2091,7 @@ static int __kvm_map_gfn(struct kvm_memslots *slots, gfn_t gfn,
void *hva = NULL;
struct page *page = KVM_UNMAPPED_PAGE;
struct kvm_memory_slot *slot = __gfn_to_memslot(slots, gfn);
+ bool protected = false;
u64 gen = slots->generation;

if (!map)
@@ -2107,12 +2108,16 @@ static int __kvm_map_gfn(struct kvm_memslots *slots, gfn_t gfn,
} else {
if (atomic)
return -EAGAIN;
- pfn = gfn_to_pfn_memslot(slot, gfn);
+ pfn = gfn_to_pfn_memslot_protected(slot, gfn, &protected);
}
if (is_error_noslot_pfn(pfn))
return -EINVAL;

- if (pfn_valid(pfn)) {
+ if (protected) {
+ if (atomic)
+ return -EAGAIN;
+ hva = ioremap_cache_force(pfn_to_hpa(pfn), PAGE_SIZE);
+ } else if (pfn_valid(pfn)) {
page = pfn_to_page(pfn);
if (atomic)
hva = kmap_atomic(page);
@@ -2133,6 +2138,7 @@ static int __kvm_map_gfn(struct kvm_memslots *slots, gfn_t gfn,
map->hva = hva;
map->pfn = pfn;
map->gfn = gfn;
+ map->protected = protected;

return 0;
}
@@ -2163,7 +2169,9 @@ static void __kvm_unmap_gfn(struct kvm_memory_slot *memslot,
if (!map->hva)
return;

- if (map->page != KVM_UNMAPPED_PAGE) {
+ if (map->protected) {
+ iounmap(map->hva);
+ } else if (map->page != KVM_UNMAPPED_PAGE) {
if (atomic)
kunmap_atomic(map->hva);
else
--
2.26.2