linux-kernel - Re: [PATCH v3 2/6] KVM: arm64: maintain per VM value for CTR

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Message-ID: <edbe3039-ed42-432e-8309-5a0a46cc2d5c@redhat.com>
Date: Wed, 29 May 2024 12:37:12 +0200
From: Eric Auger <eauger@...hat.com>
To: Sebastian Ott <sebott@...hat.com>, linux-arm-kernel@...ts.infradead.org,
 kvmarm@...ts.linux.dev, linux-kernel@...r.kernel.org
Cc: Marc Zyngier <maz@...nel.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 v3 2/6] KVM: arm64: maintain per VM value for CTR_EL0

Hi Sebastian,

On 5/14/24 09:22, Sebastian Ott wrote:
> In preparation for CTR_EL0 emulation maintain a per VM for this
s/a per VM for this register/a per VM shadow register for this latter?
> register and use it where appropriate.
> 
> Signed-off-by: Sebastian Ott <sebott@...hat.com>
> ---
>  arch/arm64/include/asm/kvm_host.h |  2 ++
>  arch/arm64/kvm/sys_regs.c         | 21 ++++++++++++++-------
>  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 212ae77eefaf..1259be5e2f3e 100644
> --- a/arch/arm64/include/asm/kvm_host.h
> +++ b/arch/arm64/include/asm/kvm_host.h
> @@ -331,6 +331,8 @@ struct kvm_arch {
>  #define KVM_ARM_ID_REG_NUM	(IDREG_IDX(sys_reg(3, 0, 0, 7, 7)) + 1)
>  	u64 id_regs[KVM_ARM_ID_REG_NUM];
>  
> +	u64 ctr_el0;
> +
>  	/* Masks for VNCR-baked sysregs */
>  	struct kvm_sysreg_masks	*sysreg_masks;
>  
> diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c
> index 41741bf4d2b2..0213c96f73f2 100644
> --- a/arch/arm64/kvm/sys_regs.c
> +++ b/arch/arm64/kvm/sys_regs.c
> @@ -219,9 +219,9 @@ void vcpu_write_sys_reg(struct kvm_vcpu *vcpu, u64 val, int reg)
>   * 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->arch.ctr_el0;
>  	u8 field;
>  
>  	if (icache)
> @@ -248,7 +248,7 @@ 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 +283,7 @@ 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) {
> @@ -1886,7 +1886,7 @@ 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 = vcpu->kvm->arch.ctr_el0;
>  	return true;
>  }
>  
> @@ -1906,7 +1906,7 @@ 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 = vcpu->kvm->arch.ctr_el0;
>  	u64 clidr;
>  	u8 loc;
>  
> @@ -1959,8 +1959,8 @@ 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 idc = !CLIDR_LOC(val) || (!CLIDR_LOUIS(val) && !CLIDR_LOUU(val));
> +	u64 ctr_el0 = vcpu->kvm->arch.ctr_el0;
>  
>  	if ((val & CLIDR_EL1_RES0) || (!(ctr_el0 & CTR_EL0_IDC) && idc))
>  		return -EINVAL;
nit: you may update the function doc comment which the extra handling of
CTR_EL0.
> @@ -3557,6 +3557,13 @@ void kvm_reset_sys_regs(struct kvm_vcpu *vcpu)
>  	struct kvm *kvm = vcpu->kvm;
>  	unsigned long i;
>  
> +	if (!kvm_vcpu_initialized(vcpu))
at this stage of the reading, why is the above check needed?
> +		/*
> +		 * Make sure CTR_EL0 is initialized before registers
> +		 * that depend on it are reset.
> +		 */
nit: the above comment explains why you need to set the shadow ctr_el0
reg  before resetting other id_regs and is not associated to the case
where (!kvm_vcpu_initialized(vcpu)) is true - at least that's my
understanding -. So I would put the comment before the check and while
at it also explain why the check is needed.
> +		kvm->arch.ctr_el0 = read_sanitised_ftr_reg(SYS_CTR_EL0);
> +
>  	for (i = 0; i < ARRAY_SIZE(sys_reg_descs); i++) {
>  		const struct sys_reg_desc *r = &sys_reg_descs[i];
>  

Thanks

Eric