On 6/4/20 7:03 PM, Anchal Agarwal wrote:

On Sat, May 30, 2020 at 07:02:01PM -0400, Boris Ostrovsky wrote:

quoted

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On 5/19/20 7:25 PM, Anchal Agarwal wrote:

quoted

Introduce a small function which re-uses shared page's PA allocated
during guest initialization time in reserve_shared_info() and not
allocate new page during resume flow.
It also  does the mapping of shared_info_page by calling
xen_hvm_init_shared_info() to use the function.

Signed-off-by: Anchal Agarwal <redacted>
---
 arch/x86/xen/enlighten_hvm.c | 7 +++++++
 arch/x86/xen/xen-ops.h       | 1 +
 2 files changed, 8 insertions(+)

diff --git a/arch/x86/xen/enlighten_hvm.c b/arch/x86/xen/enlighten_hvm.c
index e138f7de52d2..75b1ec7a0fcd 100644
--- a/arch/x86/xen/enlighten_hvm.c
+++ b/arch/x86/xen/enlighten_hvm.c

@@ -27,6 +27,13 @@

 static unsigned long shared_info_pfn;

+void xen_hvm_map_shared_info(void)
+{
+     xen_hvm_init_shared_info();
+     if (shared_info_pfn)
+             HYPERVISOR_shared_info = __va(PFN_PHYS(shared_info_pfn));
+}
+

AFAICT it is only called once so I don't see a need for new routine.

HYPERVISOR_shared_info can only be mapped in this scope without refactoring
much of the code.

Refactoring what? All am suggesting is

--- a/arch/x86/xen/suspend.c
+++ b/arch/x86/xen/suspend.c

@@ -124,7 +124,9 @@ static void xen_syscore_resume(void)

                return;
 
        /* No need to setup vcpu_info as it's already moved off */
-       xen_hvm_map_shared_info();
+       xen_hvm_init_shared_info();
+       if (shared_info_pfn)
+               HYPERVISOR_shared_info = __va(PFN_PHYS(shared_info_pfn));
 
        pvclock_resume();

quoted

And is it possible for shared_info_pfn to be NULL in resume path (which
is where this is called)?

I don't think it should be, still a sanity check but I don't think its needed there
because hibernation will fail in any case if thats the case. 

If shared_info_pfn is NULL you'd have problems long before hibernation
started. We set it in xen_hvm_guest_init() and never touch again.


In fact, I'd argue that it should be __ro_after_init.

However, HYPERVISOR_shared_info does needs to be re-mapped on resume as its been
marked to dummy address on suspend. Its also safe in case va changes.
Does the answer your question?

I wasn't arguing whether HYPERVISOR_shared_info needs to be set, I was
only saying that shared_info_pfn doesn't need to be tested.


-boris