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

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Date:   Fri, 15 Sep 2017 09:48:53 -0500
From:   Brijesh Singh <brijesh.singh@....com>
To:     Borislav Petkov <bp@...e.de>
Cc:     brijesh.singh@....com, Tom Lendacky <thomas.lendacky@....com>,
        "H. Peter Anvin" <hpa@...or.com>, Arnd Bergmann <arnd@...db.de>,
        David Laight <David.Laight@...lab.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "x86@...nel.org" <x86@...nel.org>,
        "linux-efi@...r.kernel.org" <linux-efi@...r.kernel.org>,
        "linuxppc-dev@...ts.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        Fenghua Yu <fenghua.yu@...el.com>,
        Matt Fleming <matt@...eblueprint.co.uk>,
        David Howells <dhowells@...hat.com>,
        Paul Mackerras <paulus@...ba.org>,
        Christoph Lameter <cl@...ux.com>,
        Jonathan Corbet <corbet@....net>,
        Radim Krcmár <rkrcmar@...hat.com>,
        Piotr Luc <piotr.luc@...el.com>,
        Ingo Molnar <mingo@...hat.com>,
        Dave Airlie <airlied@...hat.com>,
        Kees Cook <keescook@...omium.org>,
        Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
        Reza Arbab <arbab@...ux.vnet.ibm.com>,
        Andy Lutomirski <luto@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Laura Abbott <labbott@...hat.com>,
        Tony Luck <tony.luck@...el.com>, Ard.Biesheuvel@...or.com
Subject: Re: [RFC Part1 PATCH v3 13/17] x86/io: Unroll string I/O when SEV is
 active



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);