linux-kernel - Re: [PATCH] KVM: Switch 'requests' to be 64-bit (explicitly)

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Date:   Sun, 15 Apr 2018 13:12:42 +0000
From:   "Raslan, KarimAllah" <karahmed@...zon.de>
To:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>
CC:     "rkrcmar@...hat.com" <rkrcmar@...hat.com>,
        "pbonzini@...hat.com" <pbonzini@...hat.com>
Subject: Re: [PATCH] KVM: Switch 'requests' to be 64-bit (explicitly)

On Sun, 2018-04-15 at 00:26 +0200, KarimAllah Ahmed wrote:
> Switch 'requests' to be explicitly 64-bit and update BUILD_BUG_ON check to
> use the size of "requests" instead of the hard-coded '32'.
> 
> That gives us a bit more room again for arch-specific requests as we
> already ran out of space for x86 due to the hard-coded check.
> 
> Cc: Paolo Bonzini <pbonzini@...hat.com>
> Cc: Radim Krčmář <rkrcmar@...hat.com>
> Cc: kvm@...r.kernel.org
> Cc: linux-kernel@...r.kernel.org
> Signed-off-by: KarimAllah Ahmed <karahmed@...zon.de>
> ---
>  include/linux/kvm_host.h | 10 +++++-----
>  1 file changed, 5 insertions(+), 5 deletions(-)
> 
> diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
> index 6930c63..fe4f46b 100644
> --- a/include/linux/kvm_host.h
> +++ b/include/linux/kvm_host.h
> @@ -129,7 +129,7 @@ static inline bool is_error_page(struct page *page)
>  #define KVM_REQUEST_ARCH_BASE     8
>  
>  #define KVM_ARCH_REQ_FLAGS(nr, flags) ({ \
> -	BUILD_BUG_ON((unsigned)(nr) >= 32 - KVM_REQUEST_ARCH_BASE); \
> +	BUILD_BUG_ON((unsigned)(nr) >= (sizeof(((struct kvm_vcpu *)0)->requests) * 8) - KVM_REQUEST_ARCH_BASE); \

While looking at a completely unrelated code I realize that there 
is FIELD_SIZEOF that is doing exactly what I did. Will use it in v2.

>  	(unsigned)(((nr) + KVM_REQUEST_ARCH_BASE) | (flags)); \
>  })
>  #define KVM_ARCH_REQ(nr)           KVM_ARCH_REQ_FLAGS(nr, 0)
> @@ -223,7 +223,7 @@ struct kvm_vcpu {
>  	int vcpu_id;
>  	int srcu_idx;
>  	int mode;
> -	unsigned long requests;
> +	u64 requests;
>  	unsigned long guest_debug;
>  
>  	int pre_pcpu;
> @@ -1122,7 +1122,7 @@ static inline void kvm_make_request(int req, struct kvm_vcpu *vcpu)
>  	 * caller.  Paired with the smp_mb__after_atomic in kvm_check_request.
>  	 */
>  	smp_wmb();
> -	set_bit(req & KVM_REQUEST_MASK, &vcpu->requests);
> +	set_bit(req & KVM_REQUEST_MASK, (void *)&vcpu->requests);
>  }
>  
>  static inline bool kvm_request_pending(struct kvm_vcpu *vcpu)
> @@ -1132,12 +1132,12 @@ static inline bool kvm_request_pending(struct kvm_vcpu *vcpu)
>  
>  static inline bool kvm_test_request(int req, struct kvm_vcpu *vcpu)
>  {
> -	return test_bit(req & KVM_REQUEST_MASK, &vcpu->requests);
> +	return test_bit(req & KVM_REQUEST_MASK, (void *)&vcpu->requests);
>  }
>  
>  static inline void kvm_clear_request(int req, struct kvm_vcpu *vcpu)
>  {
> -	clear_bit(req & KVM_REQUEST_MASK, &vcpu->requests);
> +	clear_bit(req & KVM_REQUEST_MASK, (void *)&vcpu->requests);
>  }
>  
>  static inline bool kvm_check_request(int req, struct kvm_vcpu *vcpu)
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