On Tue, Jun 04, 2024 at 11:15:03AM +0200, Borislav Petkov wrote:
> On Mon, Jun 03, 2024 at 05:24:00PM -0700, H. Peter Anvin wrote:
> > Trying one more time; sorry (again) if someone receives this in duplicate.
> >
> > > > >
> > > > > diff --git a/arch/x86/kernel/relocate_kernel_64.S
> > > > > b/arch/x86/kernel/relocate_kernel_64.S
> > > > > index 56cab1bb25f5..085eef5c3904 100644
> > > > > --- a/arch/x86/kernel/relocate_kernel_64.S
> > > > > +++ b/arch/x86/kernel/relocate_kernel_64.S
> > > > > @@ -148,9 +148,10 @@ SYM_CODE_START_LOCAL_NOALIGN(identity_mapped)
> > > > > */
> > > > > movl $X86_CR4_PAE, %eax
> > > > > testq $X86_CR4_LA57, %r13
> > > > > - jz 1f
> > > > > + jz .Lno_la57
> > > > > orl $X86_CR4_LA57, %eax
> > > > > -1:
> > > > > +.Lno_la57:
> > > > > +
> > > > > movq %rax, %cr4
> >
> > If we are cleaning up this code... the above can simply be:
> >
> > andl $(X86_CR4_PAE | X86_CR4_LA54), %r13
> > movq %r13, %cr4
> >
> > %r13 is dead afterwards, and the PAE bit *will* be set in %r13 anyway.
>
> Yeah, with a proper comment. The testing of bits is not really needed.
I think it is better fit the next patch.
What about this?
>From b45fe48092abad2612c2bafbb199e4de80c99545 Mon Sep 17 00:00:00 2001
From: "Kirill A. Shutemov" <kirill.shute...@linux.intel.com>
Date: Fri, 10 Feb 2023 12:53:11 +0300
Subject: [PATCHv11.1 06/19] x86/kexec: Keep CR4.MCE set during kexec for TDX
guest
TDX guests run with MCA enabled (CR4.MCE=1b) from the very start. If
that bit is cleared during CR4 register reprogramming during boot or
kexec flows, a #VE exception will be raised which the guest kernel
cannot handle it.
Therefore, make sure the CR4.MCE setting is preserved over kexec too and
avoid raising any #VEs.
The change doesn't affect non-TDX-guest environments.
Signed-off-by: Kirill A. Shutemov <kirill.shute...@linux.intel.com>
---
arch/x86/kernel/relocate_kernel_64.S | 17 ++++++++++-------
1 file changed, 10 insertions(+), 7 deletions(-)
diff --git a/arch/x86/kernel/relocate_kernel_64.S
b/arch/x86/kernel/relocate_kernel_64.S
index 085eef5c3904..9c2cf70c5f54 100644
--- a/arch/x86/kernel/relocate_kernel_64.S
+++ b/arch/x86/kernel/relocate_kernel_64.S
@@ -5,6 +5,8 @@
*/
#include <linux/linkage.h>
+#include <linux/stringify.h>
+#include <asm/alternative.h>
#include <asm/page_types.h>
#include <asm/kexec.h>
#include <asm/processor-flags.h>
@@ -145,14 +147,15 @@ SYM_CODE_START_LOCAL_NOALIGN(identity_mapped)
* Set cr4 to a known state:
* - physical address extension enabled
* - 5-level paging, if it was enabled before
+ * - Machine check exception on TDX guest, if it was enabled before.
+ * Clearing MCE might not be allowed in TDX guests, depending on
setup.
+ *
+ * Use R13 that contains the original CR4 value, read in
relocate_kernel().
+ * PAE is always set in the original CR4.
*/
- movl $X86_CR4_PAE, %eax
- testq $X86_CR4_LA57, %r13
- jz .Lno_la57
- orl $X86_CR4_LA57, %eax
-.Lno_la57:
-
- movq %rax, %cr4
+ andl $(X86_CR4_PAE | X86_CR4_LA57), %r13d
+ ALTERNATIVE "", __stringify(orl $X86_CR4_MCE, %r13d),
X86_FEATURE_TDX_GUEST
+ movq %r13, %cr4
jmp 1f
1:
--
Kiryl Shutsemau / Kirill A. Shutemov
