linux-kernel - Re: [PATCH 4/6] KVM: x86: Split out logic to generate "readable" APIC regs mask to helper

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Date:   Sun, 08 Jan 2023 19:38:32 +0200
From:   Maxim Levitsky <mlevitsk@...hat.com>
To:     Sean Christopherson <seanjc@...gle.com>,
        Paolo Bonzini <pbonzini@...hat.com>
Cc:     kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        Marc Orr <marcorr@...gle.com>, Ben Gardon <bgardon@...gle.com>,
        Venkatesh Srinivas <venkateshs@...omium.org>
Subject: Re: [PATCH 4/6] KVM: x86: Split out logic to generate "readable"
 APIC regs mask to helper

On Sat, 2023-01-07 at 01:10 +0000, Sean Christopherson wrote:
> Move the generation of the readable APIC regs bitmask to a standalone
> helper so that VMX can use the mask for its MSR interception bitmaps.
> 
> No functional change intended.
> 
> Signed-off-by: Sean Christopherson <seanjc@...gle.com>
> ---
>  arch/x86/kvm/lapic.c | 34 +++++++++++++++++++++-------------
>  arch/x86/kvm/lapic.h |  2 ++
>  2 files changed, 23 insertions(+), 13 deletions(-)
> 
> diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
> index c49b13418638..19697fe9b2c7 100644
> --- a/arch/x86/kvm/lapic.c
> +++ b/arch/x86/kvm/lapic.c
> @@ -1529,12 +1529,9 @@ static inline struct kvm_lapic *to_lapic(struct kvm_io_device *dev)
>  #define APIC_REGS_MASK(first, count) \
>  	(APIC_REG_MASK(first) * ((1ull << (count)) - 1))
>  
> -static int kvm_lapic_reg_read(struct kvm_lapic *apic, u32 offset, int len,
> -			      void *data)
> +u64 kvm_lapic_readable_reg_mask(struct kvm_lapic *apic)
>  {
> -	unsigned char alignment = offset & 0xf;
> -	u32 result;
> -	/* this bitmask has a bit cleared for each reserved register */
> +	/* Leave bits '0' for reserved and write-only registers. */
>  	u64 valid_reg_mask =
>  		APIC_REG_MASK(APIC_ID) |
>  		APIC_REG_MASK(APIC_LVR) |
> @@ -1560,22 +1557,33 @@ static int kvm_lapic_reg_read(struct kvm_lapic *apic, u32 offset, int len,
>  	if (kvm_lapic_lvt_supported(apic, LVT_CMCI))
>  		valid_reg_mask |= APIC_REG_MASK(APIC_LVTCMCI);
>  
> -	/*
> -	 * ARBPRI, DFR, and ICR2 are not valid in x2APIC mode.  WARN if KVM
> -	 * reads ICR in x2APIC mode as it's an 8-byte register in x2APIC and
> -	 * needs to be manually handled by the caller.
> -	 */
> +	/* ARBPRI, DFR, and ICR2 are not valid in x2APIC mode. */
>  	if (!apic_x2apic_mode(apic))
>  		valid_reg_mask |= APIC_REG_MASK(APIC_ARBPRI) |
>  				  APIC_REG_MASK(APIC_DFR) |
>  				  APIC_REG_MASK(APIC_ICR2);
> -	else
> -		WARN_ON_ONCE(offset == APIC_ICR);
> +
> +	return valid_reg_mask;
> +}
> +EXPORT_SYMBOL_GPL(kvm_lapic_readable_reg_mask);
> +
> +static int kvm_lapic_reg_read(struct kvm_lapic *apic, u32 offset, int len,
> +			      void *data)
> +{
> +	unsigned char alignment = offset & 0xf;
> +	u32 result;
> +
> +	/*
> +	 * WARN if KVM reads ICR in x2APIC mode, as it's an 8-byte register in
> +	 * x2APIC and needs to be manually handled by the caller.
> +	 */
> +	WARN_ON_ONCE(apic_x2apic_mode(apic) && offset == APIC_ICR);
>  
>  	if (alignment + len > 4)
>  		return 1;
>  
> -	if (offset > 0x3f0 || !(valid_reg_mask & APIC_REG_MASK(offset)))
> +	if (offset > 0x3f0 ||
> +	    !(kvm_lapic_readable_reg_mask(apic) & APIC_REG_MASK(offset)))
>  		return 1;
>  
>  	result = __apic_read(apic, offset & ~0xf);
> diff --git a/arch/x86/kvm/lapic.h b/arch/x86/kvm/lapic.h
> index df316ede7546..0a0ea4b5dd8c 100644
> --- a/arch/x86/kvm/lapic.h
> +++ b/arch/x86/kvm/lapic.h
> @@ -146,6 +146,8 @@ int kvm_hv_vapic_msr_read(struct kvm_vcpu *vcpu, u32 msr, u64 *data);
>  int kvm_lapic_set_pv_eoi(struct kvm_vcpu *vcpu, u64 data, unsigned long len);
>  void kvm_lapic_exit(void);
>  
> +u64 kvm_lapic_readable_reg_mask(struct kvm_lapic *apic);
> +
>  #define VEC_POS(v) ((v) & (32 - 1))
>  #define REG_POS(v) (((v) >> 5) << 4)
>  

Reviewed-by: Maxim Levitsky <mlevitsk@...hat.com>

Best regards,
	Maxim Levitsky