linux-kernel - Re: [PATCH v2] KVM: x86: Check for host supported fields in shadow vmcs

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Message-ID: <535E1BD9.8000800@redhat.com>
Date:	Mon, 28 Apr 2014 11:14:01 +0200
From:	Paolo Bonzini <pbonzini@...hat.com>
To:	Bandan Das <bsd@...hat.com>, kvm@...r.kernel.org
CC:	Marcelo Tosatti <mtosatti@...hat.com>,
	Gleb Natapov <gleb@...nel.org>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] KVM: x86: Check for host supported fields in shadow
 vmcs

Il 21/04/2014 21:20, Bandan Das ha scritto:
>
> We track shadow vmcs fields through two static lists,
> one for read only and another for r/w fields. However, with
> addition of new vmcs fields, not all fields may be supported on
> all hosts. If so, copy_vmcs12_to_shadow() trying to vmwrite on
> unsupported hosts will result in a vmwrite error. For example, commit
> 36be0b9deb23161 introduced GUEST_BNDCFGS, which is not supported
> by all processors. Filter out host unsupported fields before
> letting guests use shadow vmcs
>
> Signed-off-by: Bandan Das <bsd@...hat.com>
> ---
> v2:
>   - Just compress the original lists instead of creating new ones
>   - Change commit message slightly to reflect this change
>
>  arch/x86/kvm/vmx.c | 54 ++++++++++++++++++++++++++++++++++++++++++------------
>  1 file changed, 42 insertions(+), 12 deletions(-)
>
> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
> index 7bed3e3..26a632f 100644
> --- a/arch/x86/kvm/vmx.c
> +++ b/arch/x86/kvm/vmx.c
> @@ -503,7 +503,7 @@ static inline struct vcpu_vmx *to_vmx(struct kvm_vcpu *vcpu)
>  				[number##_HIGH] = VMCS12_OFFSET(name)+4
>
>
> -static const unsigned long shadow_read_only_fields[] = {
> +static unsigned long shadow_read_only_fields[] = {
>  	/*
>  	 * We do NOT shadow fields that are modified when L0
>  	 * traps and emulates any vmx instruction (e.g. VMPTRLD,
> @@ -526,10 +526,10 @@ static const unsigned long shadow_read_only_fields[] = {
>  	GUEST_LINEAR_ADDRESS,
>  	GUEST_PHYSICAL_ADDRESS
>  };
> -static const int max_shadow_read_only_fields =
> +static int max_shadow_read_only_fields =
>  	ARRAY_SIZE(shadow_read_only_fields);
>
> -static const unsigned long shadow_read_write_fields[] = {
> +static unsigned long shadow_read_write_fields[] = {
>  	GUEST_RIP,
>  	GUEST_RSP,
>  	GUEST_CR0,
> @@ -558,7 +558,7 @@ static const unsigned long shadow_read_write_fields[] = {
>  	HOST_FS_SELECTOR,
>  	HOST_GS_SELECTOR
>  };
> -static const int max_shadow_read_write_fields =
> +static int max_shadow_read_write_fields =
>  	ARRAY_SIZE(shadow_read_write_fields);
>
>  static const unsigned short vmcs_field_to_offset_table[] = {
> @@ -3009,6 +3009,42 @@ static void free_kvm_area(void)
>  	}
>  }
>
> +static void init_vmcs_shadow_fields(void)
> +{
> +	int i, j;
> +
> +	/* No checks for read only fields yet */
> +
> +	for (i = j = 0; i < max_shadow_read_write_fields; i++) {
> +
> +		switch (shadow_read_write_fields[i]) {
> +		case GUEST_BNDCFGS:
> +			if (!vmx_mpx_supported())
> +				continue;
> +			break;
> +		default:
> +			break;
> +		}
> +
> +		if (j < i)
> +			shadow_read_write_fields[j] =
> +				shadow_read_write_fields[i];
> +		j++;
> +	}
> +	max_shadow_read_write_fields = j;
> +
> +	/* shadowed fields guest access without vmexit */
> +	for (i = 0; i < max_shadow_read_write_fields; i++) {
> +		clear_bit(shadow_read_write_fields[i],
> +			  vmx_vmwrite_bitmap);
> +		clear_bit(shadow_read_write_fields[i],
> +			  vmx_vmread_bitmap);
> +	}
> +	for (i = 0; i < max_shadow_read_only_fields; i++)
> +		clear_bit(shadow_read_only_fields[i],
> +			  vmx_vmread_bitmap);
> +}
> +
>  static __init int alloc_kvm_area(void)
>  {
>  	int cpu;
> @@ -3039,6 +3075,8 @@ static __init int hardware_setup(void)
>  		enable_vpid = 0;
>  	if (!cpu_has_vmx_shadow_vmcs())
>  		enable_shadow_vmcs = 0;
> +	if (enable_shadow_vmcs)
> +		init_vmcs_shadow_fields();
>
>  	if (!cpu_has_vmx_ept() ||
>  	    !cpu_has_vmx_ept_4levels()) {
> @@ -8817,14 +8855,6 @@ static int __init vmx_init(void)
>
>  	memset(vmx_vmread_bitmap, 0xff, PAGE_SIZE);
>  	memset(vmx_vmwrite_bitmap, 0xff, PAGE_SIZE);
> -	/* shadowed read/write fields */
> -	for (i = 0; i < max_shadow_read_write_fields; i++) {
> -		clear_bit(shadow_read_write_fields[i], vmx_vmwrite_bitmap);
> -		clear_bit(shadow_read_write_fields[i], vmx_vmread_bitmap);
> -	}
> -	/* shadowed read only fields */
> -	for (i = 0; i < max_shadow_read_only_fields; i++)
> -		clear_bit(shadow_read_only_fields[i], vmx_vmread_bitmap);
>
>  	/*
>  	 * Allow direct access to the PC debug port (it is often used for I/O
>

Applying this to kvm/master, thanks.

Paolo
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