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[Xen-devel] [PATCH 4/4] xen/acpi: Prep saved_context cr3 values.

When save_processor_state is executed it executes a bunch of
pvops calls to save the CPU state values. When it comes back
from Xen's S3 (so acpi_enter_sleep_state, which ends up calling
xen_acpi_notify_hypervisor_state), it ends up back in the
assembler code in wakeup_[32|64].S. It skips the wakeup
calls (so wakeup_pmode_return and wakeup_long64) as that has
been done in the hypervisor. Instead it continues on in
the resume_point (64-bit) or ret_point (32-bit). Most of the
calls in there are safe to be executed except when it comes to
reloading of cr3 (which it only does on 64-bit kernels). Since
they are native assembler calls and Xen expects a PV kernel to
prep those to use machine address for cr3 that is what
we are going to do. Note: that it is not Machine Frame Numbers
(those are used in the MMUEXT_NEW_BASEPTR hypercall for cr3
installation) but the machine physical address.

When the assembler code executes this mov %ebx, cr3 it ends
end up trapped in the hypervisor (traps.c) which properly now
sets the cr3 value.

Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
 drivers/xen/acpi.c |   25 +++++++++++++++++++++++++
 1 files changed, 25 insertions(+), 0 deletions(-)

diff --git a/drivers/xen/acpi.c b/drivers/xen/acpi.c
index 119d42a..25e612c 100644
--- a/drivers/xen/acpi.c
+++ b/drivers/xen/acpi.c
@@ -35,6 +35,13 @@
 #include <asm/xen/hypercall.h>
 #include <asm/xen/hypervisor.h>
+#include <xen/page.h>
+#ifdef CONFIG_X86_64
+#include <asm/suspend_64.h>
+extern struct saved_context saved_context;
 int xen_acpi_notify_hypervisor_state(u8 sleep_state,
                                     u32 pm1a_cnt, u32 pm1b_cnt)
@@ -56,7 +63,25 @@ int xen_acpi_notify_hypervisor_state(u8 sleep_state,
                     pm1a_cnt, pm1b_cnt);
                return -1;
+#ifdef CONFIG_X86_64
+       /* We do not need to anything for 32-bit kernels as the
+        * low-level calls (write to cr3) is done in the wakup code
+        * which we never execute when running under Xen.
+        */
+       {
+               unsigned long mfn;
+               /* resume_point in wakeup_64.s barrels through and does:
+                * movq    saved_context_cr3(%rax), %rbx
+                * movq    %rbx, %cr3
+                * so lets prep the values so they are OK with the
+                * hypervisor. */
+               mfn = pfn_to_mfn(PFN_DOWN(saved_context.cr3));
+               /* and back to a physical address */
+               mfn = PFN_PHYS(mfn);
+               saved_context.cr3 = mfn;
+       }
        return 1;

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