ARM, arm64: kvm: get rid of the bounce page

The HYP init bounce page is a runtime construct that ensures that the
HYP init code does not cross a page boundary. However, this is something
we can do perfectly well at build time, by aligning the code appropriately.

For arm64, we just align to 4 KB, and enforce that the code size is less
than 4 KB, regardless of the chosen page size.

For ARM, the whole code is less than 256 bytes, so we tweak the linker
script to align at a power of 2 upper bound of the code size

Note that this also fixes a benign off-by-one error in the original bounce
page code, where a bounce page would be allocated unnecessarily if the code
was exactly 1 page in size.

On ARM, it also fixes an issue with very large kernels reported by Arnd
Bergmann, where stub sections with linker emitted veneers could erroneously
trigger the size/alignment ASSERT() in the linker script.

Tested-by: Marc Zyngier <marc.zyngier@arm.com>
Reviewed-by: Marc Zyngier <marc.zyngier@arm.com>
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Signed-off-by: Will Deacon <will.deacon@arm.com>

diff --git a/arch/arm/kernel/vmlinux.lds.S b/arch/arm/kernel/vmlinux.lds.S
index b31aa73..ba65f12 100644 (file)
--- a/arch/arm/kernel/vmlinux.lds.S
+++ b/arch/arm/kernel/vmlinux.lds.S
@@ -23,11 +23,20 @@
        VMLINUX_SYMBOL(__idmap_text_start) = .;                         \
        *(.idmap.text)                                                  \
        VMLINUX_SYMBOL(__idmap_text_end) = .;                           \
-       . = ALIGN(32);                                                  \
+       . = ALIGN(1 << LOG2CEIL(__hyp_idmap_size));                     \
        VMLINUX_SYMBOL(__hyp_idmap_text_start) = .;                     \
        *(.hyp.idmap.text)                                              \
        VMLINUX_SYMBOL(__hyp_idmap_text_end) = .;
 
+/*
+ * If the HYP idmap .text section is populated, it needs to be positioned
+ * such that it will not cross a page boundary in the final output image.
+ * So align it to the section size rounded up to the next power of 2.
+ * If __hyp_idmap_size is undefined, the section will be empty so define
+ * it as 0 in that case.
+ */
+PROVIDE(__hyp_idmap_size = 0);
+
 #ifdef CONFIG_HOTPLUG_CPU
 #define ARM_CPU_DISCARD(x)
 #define ARM_CPU_KEEP(x)                x
@@ -346,8 +355,11 @@ SECTIONS
  */
 ASSERT((__proc_info_end - __proc_info_begin), "missing CPU support")
 ASSERT((__arch_info_end - __arch_info_begin), "no machine record defined")
+
 /*
- * The HYP init code can't be more than a page long.
+ * The HYP init code can't be more than a page long,
+ * and should not cross a page boundary.
  * The above comment applies as well.
  */
-ASSERT(((__hyp_idmap_text_end - __hyp_idmap_text_start) <= PAGE_SIZE), "HYP init code too big")
+ASSERT((__hyp_idmap_text_start & ~PAGE_MASK) + __hyp_idmap_size <= PAGE_SIZE,
+       "HYP init code too big or misaligned")

diff --git a/arch/arm/kvm/init.S b/arch/arm/kvm/init.S
index 3988e72..11fb1d5 100644 (file)
--- a/arch/arm/kvm/init.S
+++ b/arch/arm/kvm/init.S
@@ -157,3 +157,6 @@ target:     @ We're now in the trampoline code, switch page tables
 __kvm_hyp_init_end:
 
        .popsection
+
+       .global __hyp_idmap_size
+       .set    __hyp_idmap_size, __kvm_hyp_init_end - __kvm_hyp_init

diff --git a/arch/arm/kvm/mmu.c b/arch/arm/kvm/mmu.c
index 3e6859b..42a24d6 100644 (file)
--- a/arch/arm/kvm/mmu.c
+++ b/arch/arm/kvm/mmu.c
@@ -37,7 +37,6 @@ static pgd_t *boot_hyp_pgd;
 static pgd_t *hyp_pgd;
 static DEFINE_MUTEX(kvm_hyp_pgd_mutex);
 
-static void *init_bounce_page;
 static unsigned long hyp_idmap_start;
 static unsigned long hyp_idmap_end;
 static phys_addr_t hyp_idmap_vector;
@@ -405,9 +404,6 @@ void free_boot_hyp_pgd(void)
        if (hyp_pgd)
                unmap_range(NULL, hyp_pgd, TRAMPOLINE_VA, PAGE_SIZE);
 
-       free_page((unsigned long)init_bounce_page);
-       init_bounce_page = NULL;
-
        mutex_unlock(&kvm_hyp_pgd_mutex);
 }
 
@@ -1498,39 +1494,11 @@ int kvm_mmu_init(void)
        hyp_idmap_end = kvm_virt_to_phys(__hyp_idmap_text_end);
        hyp_idmap_vector = kvm_virt_to_phys(__kvm_hyp_init);
 
-       if ((hyp_idmap_start ^ hyp_idmap_end) & PAGE_MASK) {
-               /*
-                * Our init code is crossing a page boundary. Allocate
-                * a bounce page, copy the code over and use that.
-                */
-               size_t len = __hyp_idmap_text_end - __hyp_idmap_text_start;
-               phys_addr_t phys_base;
-
-               init_bounce_page = (void *)__get_free_page(GFP_KERNEL);
-               if (!init_bounce_page) {
-                       kvm_err("Couldn't allocate HYP init bounce page\n");
-                       err = -ENOMEM;
-                       goto out;
-               }
-
-               memcpy(init_bounce_page, __hyp_idmap_text_start, len);
-               /*
-                * Warning: the code we just copied to the bounce page
-                * must be flushed to the point of coherency.
-                * Otherwise, the data may be sitting in L2, and HYP
-                * mode won't be able to observe it as it runs with
-                * caches off at that point.
-                */
-               kvm_flush_dcache_to_poc(init_bounce_page, len);
-
-               phys_base = kvm_virt_to_phys(init_bounce_page);
-               hyp_idmap_vector += phys_base - hyp_idmap_start;
-               hyp_idmap_start = phys_base;
-               hyp_idmap_end = phys_base + len;
-
-               kvm_info("Using HYP init bounce page @%lx\n",
-                        (unsigned long)phys_base);
-       }
+       /*
+        * We rely on the linker script to ensure at build time that the HYP
+        * init code does not cross a page boundary.
+        */
+       BUG_ON((hyp_idmap_start ^ (hyp_idmap_end - 1)) & PAGE_MASK);
 
        hyp_pgd = (pgd_t *)__get_free_pages(GFP_KERNEL | __GFP_ZERO, hyp_pgd_order);
        boot_hyp_pgd = (pgd_t *)__get_free_pages(GFP_KERNEL | __GFP_ZERO, hyp_pgd_order);

diff --git a/arch/arm64/kernel/vmlinux.lds.S b/arch/arm64/kernel/vmlinux.lds.S
index 5d9d2dc..a2c2986 100644 (file)
--- a/arch/arm64/kernel/vmlinux.lds.S
+++ b/arch/arm64/kernel/vmlinux.lds.S
@@ -23,10 +23,14 @@ jiffies = jiffies_64;
 
 #define HYPERVISOR_TEXT                                        \
        /*                                              \
-        * Force the alignment to be compatible with    \
-        * the vectors requirements                     \
+        * Align to 4 KB so that                        \
+        * a) the HYP vector table is at its minimum    \
+        *    alignment of 2048 bytes                   \
+        * b) the HYP init code will not cross a page   \
+        *    boundary if its size does not exceed      \
+        *    4 KB (see related ASSERT() below)         \
         */                                             \
-       . = ALIGN(2048);                                \
+       . = ALIGN(SZ_4K);                               \
        VMLINUX_SYMBOL(__hyp_idmap_text_start) = .;     \
        *(.hyp.idmap.text)                              \
        VMLINUX_SYMBOL(__hyp_idmap_text_end) = .;       \
@@ -163,10 +167,11 @@ SECTIONS
 }
 
 /*
- * The HYP init code can't be more than a page long.
+ * The HYP init code can't be more than a page long,
+ * and should not cross a page boundary.
  */
-ASSERT(((__hyp_idmap_text_start + PAGE_SIZE) > __hyp_idmap_text_end),
-       "HYP init code too big")
+ASSERT(__hyp_idmap_text_end - (__hyp_idmap_text_start & ~(SZ_4K - 1)) <= SZ_4K,
+       "HYP init code too big or misaligned")
 
 /*
  * If padding is applied before .head.text, virt<->phys conversions will fail.