Re: [PATCH v4 2/3] x86/vmx: Update DR7 type

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 26/04/2025 8:27 am, dmkhn@xxxxxxxxx wrote:
> From: Denis Mukhin <dmukhin@xxxxxxxx>
>
> Convert the DR7 type to `unsigned int` and fix the accesses where necessary.
>
> [1] 
> https://lore.kernel.org/xen-devel/0d01646b-83e3-4a02-b365-d149d2664e73@xxxxxxxxxx/
>
> Signed-off-by: Denis Mukhin <dmukhin@xxxxxxxx>
> ---
>  xen/arch/x86/hvm/vmx/vmx.c        | 2 +-
>  xen/arch/x86/include/asm/domain.h | 2 +-
>  2 files changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/xen/arch/x86/hvm/vmx/vmx.c b/xen/arch/x86/hvm/vmx/vmx.c
> index 4883bd823d..75c6992172 100644
> --- a/xen/arch/x86/hvm/vmx/vmx.c
> +++ b/xen/arch/x86/hvm/vmx/vmx.c
> @@ -926,7 +926,7 @@ static void vmx_save_dr(struct vcpu *v)
>      v->arch.dr[3] = read_debugreg(3);
>      v->arch.dr6   = read_debugreg(6);
>      /* DR7 must be saved as it is used by vmx_restore_dr(). */
> -    __vmread(GUEST_DR7, &v->arch.dr7);
> +    v->arch.dr7 = vmread(GUEST_DR7);

Two minor points.  The = wants lining up for vertical tabulation, and ...

>  }
>  
>  static void __restore_debug_registers(struct vcpu *v)
> diff --git a/xen/arch/x86/include/asm/domain.h 
> b/xen/arch/x86/include/asm/domain.h
> index 5fc1d1e5d0..a54ef3a8c1 100644
> --- a/xen/arch/x86/include/asm/domain.h
> +++ b/xen/arch/x86/include/asm/domain.h
> @@ -595,7 +595,7 @@ struct arch_vcpu
>  
>      /* Debug registers. */
>      unsigned long dr[4];
> -    unsigned long dr7; /* Ideally int, but __vmread() needs long. */
> +    unsigned int dr7;
>      unsigned int dr6;

... these fields want switching back around now that dr7 is unsigned int.

We always access in numeric order, and they're only out-of-order for
packing reasons.

Can fix on commit.

~Andrew