Re: [Xen-devel] [PATCH] x86/svm: Use physical addresses for HSA and Host VMCB

[Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>]

On 08/16/2017 02:23 PM, Andrew Cooper wrote:
> They are only referenced by physical address (either the HSA MSR, or via
> VMSAVE/VMLOAD which take a physical operand).  Allocating xenheap hages and
> storing their virtual address is wasteful.
>
> Allocate them with domheap pages instead, taking the opportunity to suitably
> NUMA-position them.  This avoids Xen needing to perform a virt to phys
> translation on every context switch.
>
> Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>

Reviewed-by: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>

> ---
> CC: Jan Beulich <JBeulich@xxxxxxxx>
> CC: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>
> CC: Suravee Suthikulpanit <suravee.suthikulpanit@xxxxxxx>
>
> TODO at some other point: Figure out why svm_cpu_up_prepare() is reliably
> called twice for every CPU.

That's because it is called by BSP via PREPARE_CPU notifier and then by
the ASP during svm_cpu_up().

I think

diff --git a/xen/arch/x86/hvm/svm/svm.c b/xen/arch/x86/hvm/svm/svm.c
index 0dc9442..3e7b9fc 100644
--- a/xen/arch/x86/hvm/svm/svm.c
+++ b/xen/arch/x86/hvm/svm/svm.c
@@ -1538,7 +1538,7 @@ static int _svm_cpu_up(bool bsp)
         return -EINVAL;
     }
 
-    if ( (rc = svm_cpu_up_prepare(cpu)) != 0 )
+    if ( bsp && (rc = svm_cpu_up_prepare(cpu)) != 0 )
         return rc;
 
     write_efer(read_efer() | EFER_SVME);


should take care of this. I only had a quick look at intel and seems
they may have the same problem.


-boris

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