Re: Magic Page in e500v2

[Alexander Graf <agraf@suse.de>]

Hi Aashish,

On 05/21/2012 01:51 PM, Aashish Mittal wrote:
> Hi
> I'm working on KVM optimizations on Powerpc e500v2 embedded architecture. For my
> project i'm trying to increase the size of shared region mapped my Magic Page
> between host and guest for paravirtual support. I was expecting this would
> possible since we are using a TLB1 entry to map the magic page entry inside the
> host. I'm trying to increase it's size to 1MB. I've declared a shared structure
> tcache of 1MB similar to vcpu->arch.shared and trying to map it in the guest
> virtual space. The shared page earlier is now the last page of this tcache
> structure.
>
> This is the modified code :
>
> Initialization in e500.c in function kvmppc_core_vcpu_create
>
>          shared = (void*)__get_free_pages(GFP_KERNEL|__GFP_ZERO,10);
>          vcpu->arch.tcache = (void*)(shared);
>          vcpu->arch.shared = (void*)(shared + (((1<<  10)-1)<<PAGE_SHIFT));

Did you also change the shared page elements to still be within the 
first page? Otherwise the offset wouldn't fit into the immediate fields 
of the asm instructions. We can't reach as low as -1MB with all operations.


Alex

> 	
>
> void kvmppc_map_magic(struct kvm_vcpu *vcpu)
> {
> 	struct kvmppc_vcpu_e500 *vcpu_e500 = to_e500(vcpu);
> 	struct kvm_book3e_206_tlb_entry magic;
> 	ulong shared_page = ((ulong)vcpu->arch.tcache)&  PAGE_MASK;
> 	ulong page = shared_page;
> 	unsigned int stid;
> 	pfn_t pfn,pfn1;
>          int i = 0;
>
>          for(i=0;i<  1024;i++){
>            pfn1 = (pfn_t)virt_to_phys((void *)page)>>  PAGE_SHIFT;
> 	  get_page(pfn_to_page(pfn1));
>            page +=  0x1000;
> 	}
> 	
>          pfn = (pfn_t)virt_to_phys((void *)shared_page)>>  PAGE_SHIFT;
>
>
> 	preempt_disable();
> 	stid = e500_get_sid(vcpu_e500, 0, 0, 0, 0);
>
> 	magic.mas1 = MAS1_VALID | MAS1_TS | MAS1_TID(stid) |
> 		     MAS1_TSIZE(BOOK3E_PAGESZ_1M);
> 	magic.mas2 = (vcpu->arch.magic_page_ea&  0xfff00000)| MAS2_M;
>
> 	magic.mas7_3 = ((u64)pfn<<  PAGE_SHIFT) |
> 		       MAS3_SW | MAS3_SR | MAS3_UW | MAS3_UR;
>
> 	__write_host_tlbe(&magic, MAS0_TLBSEL(1) | MAS0_ESEL(tlbcam_index));
> 	preempt_enable();
> }
>
> But i'm experiencing the following error printed in the guest
>
> KVM: Live patching for a fast VM worked
> initcall kvm_guest_init+0x0/0x1f8 returned with disabled interrupts
> initcall migration_init+0x0/0x8c returned with disabled interrupts
>
> and then the guest just hangs.
>
> Does anybody have any idea how to map it correctly
>
> Thanks
>
>
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