Re: KVM: x86: ignore access permissions for hypercall patching

[Stefan Bader <stefan.bader@canonical.com>]

With this patch applied on top, I was able to boot my guest on a AMD host system.

Marcelo Tosatti wrote:
> Ignore access permissions while patching hypercall instructions. 
> Otherwise KVM injects a page fault when trying to patch vmcall 
> on read-only text regions:
> 
> Freeing initrd memory: 8843k freed
> Freeing unused kernel memory: 660k freed
> Write protecting the kernel text: 4780k
> Write protecting the kernel read-only data: 1912k
> BUG: unable to handle kernel paging request at c01292e3
> IP: [<c01292e3>] kvm_leave_lazy_mmu+0x43/0x70
> *pde = 00910067 *pte = 00129161
> Oops: 0003 [#1] SMP
> 
> CC: stable@kernel.org
> Reported-by: Stefan Bader <stefan.bader@canonical.com>
> Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>
Tested-by: Stefan Bader <stefan.bader@canonical.com>
> 
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 703f637..bf5c83f 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -3253,12 +3253,17 @@ int emulator_write_phys(struct kvm_vcpu *vcpu, gpa_t gpa,
>  static int emulator_write_emulated_onepage(unsigned long addr,
>  					   const void *val,
>  					   unsigned int bytes,
> -					   struct kvm_vcpu *vcpu)
> +					   struct kvm_vcpu *vcpu,
> +					   bool guest_initiated)
>  {
>  	gpa_t                 gpa;
>  	u32 error_code;
>  
> -	gpa = kvm_mmu_gva_to_gpa_write(vcpu, addr, &error_code);
> +
> +	if (guest_initiated)
> +		gpa = kvm_mmu_gva_to_gpa_write(vcpu, addr, &error_code);
> +	else
> +		gpa = kvm_mmu_gva_to_gpa_system(vcpu, addr, &error_code);
>  
>  	if (gpa == UNMAPPED_GVA) {
>  		kvm_inject_page_fault(vcpu, addr, error_code);
> @@ -3289,24 +3294,35 @@ mmio:
>  	return X86EMUL_CONTINUE;
>  }
>  
> -int emulator_write_emulated(unsigned long addr,
> +int __emulator_write_emulated(unsigned long addr,
>  				   const void *val,
>  				   unsigned int bytes,
> -				   struct kvm_vcpu *vcpu)
> +				   struct kvm_vcpu *vcpu,
> +				   bool guest_initiated)
>  {
>  	/* Crossing a page boundary? */
>  	if (((addr + bytes - 1) ^ addr) & PAGE_MASK) {
>  		int rc, now;
>  
>  		now = -addr & ~PAGE_MASK;
> -		rc = emulator_write_emulated_onepage(addr, val, now, vcpu);
> +		rc = emulator_write_emulated_onepage(addr, val, now, vcpu,
> +						     guest_initiated);
>  		if (rc != X86EMUL_CONTINUE)
>  			return rc;
>  		addr += now;
>  		val += now;
>  		bytes -= now;
>  	}
> -	return emulator_write_emulated_onepage(addr, val, bytes, vcpu);
> +	return emulator_write_emulated_onepage(addr, val, bytes, vcpu,
> +					       guest_initiated);
> +}
> +
> +int emulator_write_emulated(unsigned long addr,
> +				   const void *val,
> +				   unsigned int bytes,
> +				   struct kvm_vcpu *vcpu)
> +{
> +	return __emulator_write_emulated(addr, val, bytes, vcpu, true);
>  }
>  EXPORT_SYMBOL_GPL(emulator_write_emulated);
>  
> @@ -3997,7 +4013,7 @@ int kvm_fix_hypercall(struct kvm_vcpu *vcpu)
>  
>  	kvm_x86_ops->patch_hypercall(vcpu, instruction);
>  
> -	return emulator_write_emulated(rip, instruction, 3, vcpu);
> +	return __emulator_write_emulated(rip, instruction, 3, vcpu, false);
>  }
>  
>  static u64 mk_cr_64(u64 curr_cr, u32 new_val)