From: David Woodhouse <dwmw@amazon.co.uk>
Add more comments explaining what each register contains, and save the
preserve_context flag to a non-clobbered register sooner, to keep things
simpler.
Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
---
arch/x86/kernel/relocate_kernel_64.S | 17 +++++++++++++----
1 file changed, 13 insertions(+), 4 deletions(-)
diff --git a/arch/x86/kernel/relocate_kernel_64.S b/arch/x86/kernel/relocate_kernel_64.S
index e9e88c342f75..c065806884f8 100644
--- a/arch/x86/kernel/relocate_kernel_64.S
+++ b/arch/x86/kernel/relocate_kernel_64.S
@@ -100,6 +100,9 @@ SYM_CODE_START_NOALIGN(relocate_kernel)
movq %r10, CP_PA_SWAP_PAGE(%r11)
movq %rdi, CP_PA_BACKUP_PAGES_MAP(%r11)
+ /* Save the preserve_context to %r11 as swap_pages clobbers %rcx. */
+ movq %rcx, %r11
+
/* Switch to the identity mapped page tables */
movq %r9, %cr3
@@ -116,6 +119,13 @@ SYM_CODE_END(relocate_kernel)
SYM_CODE_START_LOCAL_NOALIGN(identity_mapped)
UNWIND_HINT_END_OF_STACK
+ /*
+ * %rdi indirection page
+ * %rdx start address
+ * %r11 preserve_context
+ * %r12 host_mem_enc_active
+ */
+
/* set return address to 0 if not preserving context */
pushq $0
/* store the start address on the stack */
@@ -170,8 +180,6 @@ SYM_CODE_START_LOCAL_NOALIGN(identity_mapped)
wbinvd
.Lsme_off:
- /* Save the preserve_context to %r11 as swap_pages clobbers %rcx. */
- movq %rcx, %r11
call swap_pages
/*
@@ -183,13 +191,14 @@ SYM_CODE_START_LOCAL_NOALIGN(identity_mapped)
movq %cr3, %rax
movq %rax, %cr3
+ testq %r11, %r11 /* preserve_context */
+ jnz .Lrelocate
+
/*
* set all of the registers to known values
* leave %rsp alone
*/
- testq %r11, %r11
- jnz .Lrelocate
xorl %eax, %eax
xorl %ebx, %ebx
xorl %ecx, %ecx
--
2.44.0On Sun, 2024-11-03 at 05:35 +0000, David Woodhouse wrote: > From: David Woodhouse <dwmw@amazon.co.uk> > > Add more comments explaining what each register contains, and save the > preserve_context flag to a non-clobbered register sooner, to keep things > simpler. > > Signed-off-by: David Woodhouse <dwmw@amazon.co.uk> > --- > arch/x86/kernel/relocate_kernel_64.S | 17 +++++++++++++---- > 1 file changed, 13 insertions(+), 4 deletions(-) > > diff --git a/arch/x86/kernel/relocate_kernel_64.S b/arch/x86/kernel/relocate_kernel_64.S > index e9e88c342f75..c065806884f8 100644 > --- a/arch/x86/kernel/relocate_kernel_64.S > +++ b/arch/x86/kernel/relocate_kernel_64.S > @@ -100,6 +100,9 @@ SYM_CODE_START_NOALIGN(relocate_kernel) > movq %r10, CP_PA_SWAP_PAGE(%r11) > movq %rdi, CP_PA_BACKUP_PAGES_MAP(%r11) > > + /* Save the preserve_context to %r11 as swap_pages clobbers %rcx. */ > + movq %rcx, %r11 > + Seems moving this here won't break anything. From functionality's perspective there's no need move this here, but fine to me since the move is needed for the sake of adding the comment (below) to identity_mapped. > /* Switch to the identity mapped page tables */ > movq %r9, %cr3 > > @@ -116,6 +119,13 @@ SYM_CODE_END(relocate_kernel) > > SYM_CODE_START_LOCAL_NOALIGN(identity_mapped) > UNWIND_HINT_END_OF_STACK > + /* > + * %rdi indirection page > + * %rdx start address > + * %r11 preserve_context > + * %r12 host_mem_enc_active > + */ > + I think adding this comment is the main purpose of this patch. Since we have listed 4 regs in the comment, how about also add an entry for %r13? Something like: %r13 original CR4 when relocate_kernel() is invoked Yeah this is kinda mentioned in later code but it seems it's more complete if we also mention %r13 here. Anyway, I suppose adding this comment is kinda helpful, so: Acked-by: Kai Huang <kai.huang@intel.com>
On Tue, 2024-11-05 at 10:00 +0000, Huang, Kai wrote: > On Sun, 2024-11-03 at 05:35 +0000, David Woodhouse wrote: > > From: David Woodhouse <dwmw@amazon.co.uk> > > > > Add more comments explaining what each register contains, and save the > > preserve_context flag to a non-clobbered register sooner, to keep things > > simpler. > > > > Signed-off-by: David Woodhouse <dwmw@amazon.co.uk> > > --- > > arch/x86/kernel/relocate_kernel_64.S | 17 +++++++++++++---- > > 1 file changed, 13 insertions(+), 4 deletions(-) > > > > diff --git a/arch/x86/kernel/relocate_kernel_64.S b/arch/x86/kernel/relocate_kernel_64.S > > index e9e88c342f75..c065806884f8 100644 > > --- a/arch/x86/kernel/relocate_kernel_64.S > > +++ b/arch/x86/kernel/relocate_kernel_64.S > > @@ -100,6 +100,9 @@ SYM_CODE_START_NOALIGN(relocate_kernel) > > movq %r10, CP_PA_SWAP_PAGE(%r11) > > movq %rdi, CP_PA_BACKUP_PAGES_MAP(%r11) > > > > + /* Save the preserve_context to %r11 as swap_pages clobbers %rcx. */ > > + movq %rcx, %r11 > > + > > Seems moving this here won't break anything. From functionality's perspective > there's no need move this here, but fine to me since the move is needed for the > sake of adding the comment (below) to identity_mapped. I believe I did actually use %rcx in the debug code I added later, didn't I? > > /* Switch to the identity mapped page tables */ > > movq %r9, %cr3 > > > > @@ -116,6 +119,13 @@ SYM_CODE_END(relocate_kernel) > > > > SYM_CODE_START_LOCAL_NOALIGN(identity_mapped) > > UNWIND_HINT_END_OF_STACK > > + /* > > + * %rdi indirection page > > + * %rdx start address > > + * %r11 preserve_context > > + * %r12 host_mem_enc_active > > + */ > > + > > I think adding this comment is the main purpose of this patch. Since we have > listed 4 regs in the comment, how about also add an entry for %r13? > > Something like: > > %r13 original CR4 when relocate_kernel() is invoked > > Yeah this is kinda mentioned in later code but it seems it's more complete if we > also mention %r13 here. Ack, I'll add that too. Thanks. > Anyway, I suppose adding this comment is kinda helpful, so: > > Acked-by: Kai Huang <kai.huang@intel.com> >
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