linux-kernel - Re: [PATCH 2/4] KVM: arm64: maintain per VM value for CTR

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Message-ID: <86frvpshno.wl-maz@kernel.org>
Date: Sat, 13 Apr 2024 11:04:11 +0100
From: Marc Zyngier <maz@...nel.org>
To: Sebastian Ott <sebott@...hat.com>
Cc: linux-arm-kernel@...ts.infradead.org,
	kvmarm@...ts.linux.dev,
	linux-kernel@...r.kernel.org,
	Oliver Upton <oliver.upton@...ux.dev>,
	James Morse <james.morse@....com>,
	Suzuki K Poulose <suzuki.poulose@....com>,
	Catalin Marinas <catalin.marinas@....com>,
	Will Deacon <will@...nel.org>
Subject: Re: [PATCH 2/4] KVM: arm64: maintain per VM value for CTR_EL0

On Fri, 05 Apr 2024 13:01:06 +0100,
Sebastian Ott <sebott@...hat.com> wrote:
> 
> In preparation for CTR_EL0 emulation maintain a per VM for this
> register and use it where appropriate.
> 
> Signed-off-by: Sebastian Ott <sebott@...hat.com>
> ---
>  arch/arm64/include/asm/kvm_host.h |  1 +
>  arch/arm64/kvm/sys_regs.c         | 22 +++++++++++++++-------
>  2 files changed, 16 insertions(+), 7 deletions(-)
> 
> diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
> index 9e8a496fb284..481216febb46 100644
> --- a/arch/arm64/include/asm/kvm_host.h
> +++ b/arch/arm64/include/asm/kvm_host.h
> @@ -318,6 +318,7 @@ struct kvm_arch {
>  
>  	/* PMCR_EL0.N value for the guest */
>  	u8 pmcr_n;
> +	u64 ctr_el0;
>  
>  	/* Iterator for idreg debugfs */
>  	u8	idreg_debugfs_iter;

Please consider the alignment of the fields. This leaves a 7 byte hole
that could be avoided (yes, I'm on a mission to reduce the size of the
various structures, because they are absolute pigs).

> diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c
> index 131f5b0ca2b9..4d29b1a0842d 100644
> --- a/arch/arm64/kvm/sys_regs.c
> +++ b/arch/arm64/kvm/sys_regs.c
> @@ -215,13 +215,21 @@ void vcpu_write_sys_reg(struct kvm_vcpu *vcpu, u64 val, int reg)
>  /* CSSELR values; used to index KVM_REG_ARM_DEMUX_ID_CCSIDR */
>  #define CSSELR_MAX 14
>  
> +static u64 kvm_get_ctr_el0(struct kvm *kvm)
> +{
> +	if (kvm->arch.ctr_el0)
> +		return kvm->arch.ctr_el0;

Is this relying on some bits not being 0?

> +
> +	return read_sanitised_ftr_reg(SYS_CTR_EL0);

Why isn't the shadow value always populated?

> +}
> +
>  /*
>   * Returns the minimum line size for the selected cache, expressed as
>   * Log2(bytes).
>   */
> -static u8 get_min_cache_line_size(bool icache)
> +static u8 get_min_cache_line_size(struct kvm *kvm, bool icache)
>  {
> -	u64 ctr = read_sanitised_ftr_reg(SYS_CTR_EL0);
> +	u64 ctr = kvm_get_ctr_el0(kvm);
>  	u8 field;
>  
>  	if (icache)
> @@ -248,7 +256,7 @@ static u32 get_ccsidr(struct kvm_vcpu *vcpu, u32 csselr)
>  	if (vcpu->arch.ccsidr)
>  		return vcpu->arch.ccsidr[csselr];
>  
> -	line_size = get_min_cache_line_size(csselr & CSSELR_EL1_InD);
> +	line_size = get_min_cache_line_size(vcpu->kvm, csselr & CSSELR_EL1_InD);
>  
>  	/*
>  	 * Fabricate a CCSIDR value as the overriding value does not exist.
> @@ -283,7 +291,7 @@ static int set_ccsidr(struct kvm_vcpu *vcpu, u32 csselr, u32 val)
>  	u32 i;
>  
>  	if ((val & CCSIDR_EL1_RES0) ||
> -	    line_size < get_min_cache_line_size(csselr & CSSELR_EL1_InD))
> +	    line_size < get_min_cache_line_size(vcpu->kvm, csselr & CSSELR_EL1_InD))
>  		return -EINVAL;
>  
>  	if (!ccsidr) {
> @@ -1862,7 +1870,7 @@ static bool access_ctr(struct kvm_vcpu *vcpu, struct sys_reg_params *p,
>  	if (p->is_write)
>  		return write_to_read_only(vcpu, p, r);
>  
> -	p->regval = read_sanitised_ftr_reg(SYS_CTR_EL0);
> +	p->regval = kvm_get_ctr_el0(vcpu->kvm);
>  	return true;
>  }
>  
> @@ -1882,7 +1890,7 @@ static bool access_clidr(struct kvm_vcpu *vcpu, struct sys_reg_params *p,
>   */
>  static u64 reset_clidr(struct kvm_vcpu *vcpu, const struct sys_reg_desc *r)
>  {
> -	u64 ctr_el0 = read_sanitised_ftr_reg(SYS_CTR_EL0);
> +	u64 ctr_el0 = kvm_get_ctr_el0(vcpu->kvm);
>  	u64 clidr;
>  	u8 loc;
>  
> @@ -1935,7 +1943,7 @@ static u64 reset_clidr(struct kvm_vcpu *vcpu, const struct sys_reg_desc *r)
>  static int set_clidr(struct kvm_vcpu *vcpu, const struct sys_reg_desc *rd,
>  		      u64 val)
>  {
> -	u64 ctr_el0 = read_sanitised_ftr_reg(SYS_CTR_EL0);
> +	u64 ctr_el0 = kvm_get_ctr_el0(vcpu->kvm);
>  	u64 idc = !CLIDR_LOC(val) || (!CLIDR_LOUIS(val) && !CLIDR_LOUU(val));
>  
>  	if ((val & CLIDR_EL1_RES0) || (!(ctr_el0 & CTR_EL0_IDC) && idc))

Thanks,

	M.

-- 
Without deviation from the norm, progress is not possible.