linux-kernel - Re: [PATCH v9 6/7] arm64: kvm: Set Virtual SError Exception Syndrome for guest

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Date:   Tue, 23 Jan 2018 19:07:50 +0000
From:   James Morse <james.morse@....com>
To:     Dongjiu Geng <gengdongjiu@...wei.com>
CC:     christoffer.dall@...aro.org, marc.zyngier@....com,
        linux@...linux.org.uk, catalin.marinas@....com, rjw@...ysocki.net,
        bp@...en8.de, robert.moore@...el.com, lv.zheng@...el.com,
        corbet@....net, will.deacon@....com, linux-doc@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        kvmarm@...ts.cs.columbia.edu, linux-acpi@...r.kernel.org,
        devel@...ica.org, huangshaoyu@...wei.com
Subject: Re: [PATCH v9 6/7] arm64: kvm: Set Virtual SError Exception Syndrome
 for guest

Hi Dongjiu Geng,

On 06/01/18 16:02, Dongjiu Geng wrote:
> RAS Extension add a VSESR_EL2 register which can provide
> the syndrome value reported to software on taking a virtual
> SError interrupt exception. This patch supports to specify
> this Syndrome.
> 
> In the RAS Extensions we can not set all-zero syndrome value
> for SError, which means 'RAS error: Uncategorized' instead of
> 'no valid ISS'. So set it to IMPLEMENTATION DEFINED syndrome
> by default.
> 
> We also need to support userspace to specify a valid syndrome
> value, Because in some case, the recovery is driven by userspace.
> This patch can support that userspace specify it.
> 
> In the guest/host world switch, restore this value to VSESR_EL2
> only when HCR_EL2.VSE is set. This value no need to be saved
> because it is stale vale when guest exit.

A version of this patch has been queued by Catalin.

Now that the cpufeature bits are queued, I think this can be split up into two
separate series for v4.16-rc1, one to tackle NOTIFY_SEI and the associated
plumbing. The second for the KVM 'make SError pending' API.


> Signed-off-by: Dongjiu Geng <gengdongjiu@...wei.com>
> [Set an impdef ESR for Virtual-SError]
> Signed-off-by: James Morse <james.morse@....com>

I didn't sign-off this patch. If you pick some bits from another version and
want to credit someone else you can 'CC:' them or just mention it in the
commit-message.


> diff --git a/arch/arm64/include/asm/sysreg.h b/arch/arm64/include/asm/sysreg.h
> index 47b967d..3b035cc 100644
> --- a/arch/arm64/include/asm/sysreg.h
> +++ b/arch/arm64/include/asm/sysreg.h
> @@ -86,6 +86,9 @@
>  #define REG_PSTATE_PAN_IMM		sys_reg(0, 0, 4, 0, 4)
>  #define REG_PSTATE_UAO_IMM		sys_reg(0, 0, 4, 0, 3)
>  
> +/* virtual SError exception syndrome register */
> +#define REG_VSESR_EL2                  sys_reg(3, 4, 5, 2, 3)

Irrelevant-Nit: sys-regs usually have a 'SYS_' prefix, and are in instruction
encoding order lower down the file.

(These PSTATE PAN things are a bit odd as they were used to generate and
instruction before the fancy {read,write}_sysreg() helpers were added).


>  #define SET_PSTATE_PAN(x) __emit_inst(0xd5000000 | REG_PSTATE_PAN_IMM |	\
>  				      (!!x)<<8 | 0x1f)
>  #define SET_PSTATE_UAO(x) __emit_inst(0xd5000000 | REG_PSTATE_UAO_IMM |	\
> diff --git a/arch/arm64/kvm/guest.c b/arch/arm64/kvm/guest.c
> index 738ae90..ffad42b 100644
> --- a/arch/arm64/kvm/guest.c
> +++ b/arch/arm64/kvm/guest.c
> @@ -279,7 +279,16 @@ int kvm_arch_vcpu_ioctl_set_sregs(struct kvm_vcpu *vcpu,
>  
>  int kvm_arm_set_sei_esr(struct kvm_vcpu *vcpu, u32 *syndrome)

Bits of this are spread between patches 5 and 6. If you put them in the other
order this wouldn't happen.

(but after a rebase most of this patch should disappear)

>  {
> -	return -EINVAL;
> +	u64 reg = *syndrome;
> +
> +	/* inject virtual system Error or asynchronous abort */
> +	kvm_inject_vabt(vcpu);

So this writes an impdef ESR, because its the existing code-path in KVM.


> +	if (reg)
> +		/* set vsesr_el2[24:0] with value that user space specified */
> +		kvm_vcpu_set_vsesr(vcpu, reg & ESR_ELx_ISS_MASK);

And then you overwrite it. Which is a bit odd as there is a helper to do both in
one go:


> +
> +	return 0;
>  }

>  int __attribute_const__ kvm_target_cpu(void)

> diff --git a/arch/arm64/kvm/inject_fault.c b/arch/arm64/kvm/inject_fault.c
> index 3556715..fb94b5e 100644
> --- a/arch/arm64/kvm/inject_fault.c
> +++ b/arch/arm64/kvm/inject_fault.c
> @@ -246,14 +246,25 @@ void kvm_inject_undefined(struct kvm_vcpu *vcpu)
>  		inject_undef64(vcpu);
>  }
>  
> +static void pend_guest_serror(struct kvm_vcpu *vcpu, u64 esr)
> +{
> +	kvm_vcpu_set_vsesr(vcpu, esr);
> +	vcpu_set_hcr(vcpu, vcpu_get_hcr(vcpu) | HCR_VSE);
> +}

How come you don't use this in kvm_arm_set_sei_esr()?



Thanks,

James