Re: [PATCH 2/3] KVM/MIPS32: Wrap calls to gfn_to_pfn() with srcu_read_lock/unlock()

[Gleb Natapov <gleb@redhat.com>]

On Fri, May 17, 2013 at 02:25:11PM -0700, Sanjay Lal wrote:
> - As suggested by Gleb, wrap calls to gfn_to_pfn() with srcu_read_lock/unlock().
>   Memory slots should be acccessed from a SRCU read section.
> - kvm_mips_map_page() now returns an error code to it's callers, instead of calling panic()
>  if it cannot find a mapping for a particular gfn.
> 
> Signed-off-by: Sanjay Lal <sanjayl@kymasys.com>
> ---
>  arch/mips/kvm/kvm_tlb.c | 36 +++++++++++++++++++++++++++---------
>  1 file changed, 27 insertions(+), 9 deletions(-)
> 
> diff --git a/arch/mips/kvm/kvm_tlb.c b/arch/mips/kvm/kvm_tlb.c
> index 89511a9..ab2e9b0 100644
> --- a/arch/mips/kvm/kvm_tlb.c
> +++ b/arch/mips/kvm/kvm_tlb.c
> @@ -16,7 +16,10 @@
>  #include <linux/mm.h>
>  #include <linux/delay.h>
>  #include <linux/module.h>
> +#include <linux/bootmem.h>
Is this include still needed now when you export min_low_pfn in
mips_ksyms.c?

>  #include <linux/kvm_host.h>
> +#include <linux/srcu.h>
> +
>  
>  #include <asm/cpu.h>
>  #include <asm/bootinfo.h>
> @@ -169,21 +172,27 @@ void kvm_mips_dump_shadow_tlbs(struct kvm_vcpu *vcpu)
>  	}
>  }
>  
> -static void kvm_mips_map_page(struct kvm *kvm, gfn_t gfn)
> +static int kvm_mips_map_page(struct kvm *kvm, gfn_t gfn)
>  {
> +	int srcu_idx, err = 0;
>  	pfn_t pfn;
>  
>  	if (kvm->arch.guest_pmap[gfn] != KVM_INVALID_PAGE)
> -		return;
> +		return 0;
>  
> +        srcu_idx = srcu_read_lock(&kvm->srcu);
>  	pfn = kvm_mips_gfn_to_pfn(kvm, gfn);
>  
>  	if (kvm_mips_is_error_pfn(pfn)) {
> -		panic("Couldn't get pfn for gfn %#" PRIx64 "!\n", gfn);
> +		kvm_err("Couldn't get pfn for gfn %#" PRIx64 "!\n", gfn);
> +		err = -EFAULT;
> +		goto out;
>  	}
>  
>  	kvm->arch.guest_pmap[gfn] = pfn;
> -	return;
> +out:
> +	srcu_read_unlock(&kvm->srcu, srcu_idx);
> +	return err;
>  }
>  
>  /* Translate guest KSEG0 addresses to Host PA */
> @@ -207,7 +216,10 @@ unsigned long kvm_mips_translate_guest_kseg0_to_hpa(struct kvm_vcpu *vcpu,
>  			gva);
>  		return KVM_INVALID_PAGE;
>  	}
> -	kvm_mips_map_page(vcpu->kvm, gfn);
> +
> +	if (kvm_mips_map_page(vcpu->kvm, gfn) < 0)
> +		return KVM_INVALID_ADDR;
> +
>  	return (kvm->arch.guest_pmap[gfn] << PAGE_SHIFT) + offset;
>  }
>  
> @@ -310,8 +322,11 @@ int kvm_mips_handle_kseg0_tlb_fault(unsigned long badvaddr,
>  	even = !(gfn & 0x1);
>  	vaddr = badvaddr & (PAGE_MASK << 1);
>  
> -	kvm_mips_map_page(vcpu->kvm, gfn);
> -	kvm_mips_map_page(vcpu->kvm, gfn ^ 0x1);
> +	if (kvm_mips_map_page(vcpu->kvm, gfn) < 0)
> +		return -1;
> +
> +	if (kvm_mips_map_page(vcpu->kvm, gfn ^ 0x1) < 0)
> +		return -1;
>  
>  	if (even) {
>  		pfn0 = kvm->arch.guest_pmap[gfn];
> @@ -389,8 +404,11 @@ kvm_mips_handle_mapped_seg_tlb_fault(struct kvm_vcpu *vcpu,
>  		pfn0 = 0;
>  		pfn1 = 0;
>  	} else {
> -		kvm_mips_map_page(kvm, mips3_tlbpfn_to_paddr(tlb->tlb_lo0) >> PAGE_SHIFT);
> -		kvm_mips_map_page(kvm, mips3_tlbpfn_to_paddr(tlb->tlb_lo1) >> PAGE_SHIFT);
> +		if (kvm_mips_map_page(kvm, mips3_tlbpfn_to_paddr(tlb->tlb_lo0) >> PAGE_SHIFT) < 0)
> +			return -1;
> +
> +		if (kvm_mips_map_page(kvm, mips3_tlbpfn_to_paddr(tlb->tlb_lo1) >> PAGE_SHIFT) < 0)
> +			return -1;
>  
>  		pfn0 = kvm->arch.guest_pmap[mips3_tlbpfn_to_paddr(tlb->tlb_lo0) >> PAGE_SHIFT];
>  		pfn1 = kvm->arch.guest_pmap[mips3_tlbpfn_to_paddr(tlb->tlb_lo1) >> PAGE_SHIFT];
> -- 
> 1.7.11.3

--
			Gleb.