[RFC Part1 PATCH v3 13/17] x86/io: Unroll string I/O when SEV is active

[Brijesh Singh]

On 09/15/2017 09:40 AM, Borislav Petkov wrote:
> I need to figure out the include hell first.

I am working with slightly newer patch sets -- in that patch Tom has
moved the sev_active() definition in arch/x86/mm/mem_encrypt.c and I
have no issue using your recommended (since I no longer need the include
path changes).

But in my quick run I did found a runtime issue, it seems enabling the static
key in sme_enable is too early. Guest reboots as soon as it tries to enable
the key.

I see the similar issue with non SEV guest with my simple patch below.
Guest will reboot as soon as it tries to enable the key.

--- a/arch/x86/kernel/head64.c
+++ b/arch/x86/kernel/head64.c
@@ -40,6 +40,8 @@ pmdval_t early_pmd_flags = __PAGE_KERNEL_LARGE & ~(_PAGE_GLOBAL | _PAGE_NX);
  
  #define __head __section(.head.text)
  
+DEFINE_STATIC_KEY_FALSE(__testme);
+
  static void __head *fixup_pointer(void *ptr, unsigned long physaddr)
  {
         return ptr - (void *)_text + (void *)physaddr;
@@ -71,6 +73,8 @@ unsigned long __head __startup_64(unsigned long physaddr,
         if (load_delta & ~PMD_PAGE_MASK)
                 for (;;);
  
+       static_branch_enable(&__testme);
+
         /* Activate Secure Memory Encryption (SME) if supported and enabled */
         sme_enable(bp);