Re: [Xen-devel] [PATCH 04/18] xen/arm: Save HCR_EL2 when a guest took the SError

[Stefano Stabellini <sstabellini@xxxxxxxxxx>]

On Mon, 13 Mar 2017, Wei Chen wrote:
> The HCR_EL2.VSE (HCR.VA for aarch32) bit can be used to generate a
> virtual abort to guest. The HCR_EL2.VSE bit has a peculiar feature
> of getting cleared when the guest has taken the abort (this is the
> only bit that behaves as such in HCR_EL2 register).
> 
> This means that if we set the HCR_EL2.VSE bit to signal such an abort,
> we must preserve it in the guest context until it disappears from
> HCR_EL2, and at which point it must be cleared from the context. This
> is achieved by reading back from HCR_EL2 until the guest takes the
> fault.
> 
> If we preserved a pending VSE in guest context, we have to restore
> it to HCR_EL2 when context switch to this guest. This is achieved
> by writing saved HCR_EL2 value in guest context back to HCR_EL2
> register before return to guest. This had been done by the patch
> of "Restore HCR_EL2 register".
> 
> Signed-off-by: Wei Chen <Wei.Chen@xxxxxxx>

Reviewed-by: Stefano Stabellini <sstabellini@xxxxxxxxxx>

> ---
>  xen/arch/arm/traps.c | 11 +++++++++++
>  1 file changed, 11 insertions(+)
> 
> diff --git a/xen/arch/arm/traps.c b/xen/arch/arm/traps.c
> index 9792d02..476e2be 100644
> --- a/xen/arch/arm/traps.c
> +++ b/xen/arch/arm/traps.c
> @@ -2641,7 +2641,18 @@ static void do_trap_smc(struct cpu_user_regs *regs, 
> const union hsr hsr)
>  static void enter_hypervisor_head(struct cpu_user_regs *regs)
>  {
>      if ( guest_mode(regs) )
> +    {
> +        /*
> +         * If we pended a virtual abort, preserve it until it gets cleared.
> +         * See ARM ARM DDI 0487A.j D1.14.3 (Virtual Interrupts) for details,
> +         * but the crucial bit is "On taking a vSError interrupt, HCR_EL2.VSE
> +         * (alias of HCR.VA) is cleared to 0."
> +         */
> +        if ( current->arch.hcr_el2 & HCR_VA )
> +            current->arch.hcr_el2 = READ_SYSREG(HCR_EL2);
> +
>          gic_clear_lrs(current);
> +    }
>  }
>  
>  asmlinkage void do_trap_hypervisor(struct cpu_user_regs *regs)
> -- 
> 2.7.4
> 
> 
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> 

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