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Subject[PATCH v2 4/5] x86/boot: Rework reserve_real_mode() to allow multiple tries
Date
If reserve_real_mode() fails, panicing immediately means we're
doomed. Make it safe to try more than once to allocate the
trampoline:

- Degrade a failure from panic() to pr_info(). (If we make it to
setup_real_mode() without reserving the trampoline, we'll panic
them.)

- Factor out helpers so that platform code can supply a specific
address to try.

- Warn if reserve_real_mode() is called after we're done with the
memblock allocator. If that were to happen, we would behave
unpredictably.

Signed-off-by: Andy Lutomirski <luto@kernel.org>
---
arch/x86/include/asm/realmode.h | 9 +++++++++
arch/x86/realmode/init.c | 29 +++++++++++++++++++++--------
2 files changed, 30 insertions(+), 8 deletions(-)

diff --git a/arch/x86/include/asm/realmode.h b/arch/x86/include/asm/realmode.h
index 8d6777724ba4..b2988c0ed829 100644
--- a/arch/x86/include/asm/realmode.h
+++ b/arch/x86/include/asm/realmode.h
@@ -58,6 +58,15 @@ extern unsigned char boot_gdt[];
extern unsigned char secondary_startup_64[];
#endif

+static inline size_t real_mode_size_needed(void)
+{
+ if (real_mode_header)
+ return 0; /* already allocated. */
+
+ return ALIGN(real_mode_blob_end - real_mode_blob, PAGE_SIZE);
+}
+
+void set_real_mode_mem(phys_addr_t mem, size_t size);
void reserve_real_mode(void);

#endif /* _ARCH_X86_REALMODE_H */
diff --git a/arch/x86/realmode/init.c b/arch/x86/realmode/init.c
index 747b71e8f547..5db706f14111 100644
--- a/arch/x86/realmode/init.c
+++ b/arch/x86/realmode/init.c
@@ -1,4 +1,5 @@
#include <linux/io.h>
+#include <linux/slab.h>
#include <linux/memblock.h>

#include <asm/cacheflush.h>
@@ -12,22 +13,34 @@ u32 *trampoline_cr4_features;
/* Hold the pgd entry used on booting additional CPUs */
pgd_t trampoline_pgd_entry;

+void __init set_real_mode_mem(phys_addr_t mem, size_t size)
+{
+ void *base = __va(mem);
+
+ real_mode_header = (struct real_mode_header *) base;
+ printk(KERN_DEBUG "Base memory trampoline at [%p] %llx size %zu\n",
+ base, (unsigned long long)mem, size);
+}
+
void __init reserve_real_mode(void)
{
phys_addr_t mem;
- unsigned char *base;
- size_t size = PAGE_ALIGN(real_mode_blob_end - real_mode_blob);
+ size_t size = real_mode_size_needed();
+
+ if (!size)
+ return;
+
+ WARN_ON(slab_is_available());

/* Has to be under 1M so we can execute real-mode AP code. */
mem = memblock_find_in_range(0, 1<<20, size, PAGE_SIZE);
- if (!mem)
- panic("Cannot allocate trampoline\n");
+ if (!mem) {
+ pr_info("No sub-1M memory is available for the trampoline\n");
+ return;
+ }

- base = __va(mem);
memblock_reserve(mem, size);
- real_mode_header = (struct real_mode_header *) base;
- printk(KERN_DEBUG "Base memory trampoline at [%p] %llx size %zu\n",
- base, (unsigned long long)mem, size);
+ set_real_mode_mem(mem, size);
}

static void __init setup_real_mode(void)
--
2.7.4
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