linux-kernel - Re: [PATCH 02/16] KVM: x86: Remove separate "bit" defines for page fault error code masks

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Date: Thu, 29 Feb 2024 05:43:55 -0800
From: Dongli Zhang <dongli.zhang@...cle.com>
To: Sean Christopherson <seanjc@...gle.com>,
        Paolo Bonzini <pbonzini@...hat.com>
Cc: kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        Yan Zhao <yan.y.zhao@...el.com>,
        Isaku Yamahata <isaku.yamahata@...el.com>,
        Michael Roth <michael.roth@....com>,
        Yu Zhang <yu.c.zhang@...ux.intel.com>,
        Chao Peng <chao.p.peng@...ux.intel.com>, Fuad Tabba <tabba@...gle.com>,
        David Matlack <dmatlack@...gle.com>
Subject: Re: [PATCH 02/16] KVM: x86: Remove separate "bit" defines for page
 fault error code masks

I remember I read somewhere suggesting not to change the headers in selftest.

Just double-check if there is requirement to edit
tools/testing/selftests/kvm/include/x86_64/processor.h.

Dongli Zhang

On 2/27/24 18:41, Sean Christopherson wrote:
> Open code the bit number directly in the PFERR_* masks and drop the
> intermediate PFERR_*_BIT defines, as having to bounce through two macros
> just to see which flag corresponds to which bit is quite annoying, as is
> having to define two macros just to add recognition of a new flag.
> 
> Use ilog2() to derive the bit in permission_fault(), the one function that
> actually needs the bit number (it does clever shifting to manipulate flags
> in order to avoid conditional branches).
> 
> No functional change intended.
> 
> Signed-off-by: Sean Christopherson <seanjc@...gle.com>
> ---
>  arch/x86/include/asm/kvm_host.h | 32 ++++++++++----------------------
>  arch/x86/kvm/mmu.h              |  4 ++--
>  2 files changed, 12 insertions(+), 24 deletions(-)
> 
> diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
> index aaf5a25ea7ed..88cc523bafa8 100644
> --- a/arch/x86/include/asm/kvm_host.h
> +++ b/arch/x86/include/asm/kvm_host.h
> @@ -254,28 +254,16 @@ enum x86_intercept_stage;
>  	KVM_GUESTDBG_INJECT_DB | \
>  	KVM_GUESTDBG_BLOCKIRQ)
>  
> -
> -#define PFERR_PRESENT_BIT 0
> -#define PFERR_WRITE_BIT 1
> -#define PFERR_USER_BIT 2
> -#define PFERR_RSVD_BIT 3
> -#define PFERR_FETCH_BIT 4
> -#define PFERR_PK_BIT 5
> -#define PFERR_SGX_BIT 15
> -#define PFERR_GUEST_FINAL_BIT 32
> -#define PFERR_GUEST_PAGE_BIT 33
> -#define PFERR_IMPLICIT_ACCESS_BIT 48
> -
> -#define PFERR_PRESENT_MASK	BIT(PFERR_PRESENT_BIT)
> -#define PFERR_WRITE_MASK	BIT(PFERR_WRITE_BIT)
> -#define PFERR_USER_MASK		BIT(PFERR_USER_BIT)
> -#define PFERR_RSVD_MASK		BIT(PFERR_RSVD_BIT)
> -#define PFERR_FETCH_MASK	BIT(PFERR_FETCH_BIT)
> -#define PFERR_PK_MASK		BIT(PFERR_PK_BIT)
> -#define PFERR_SGX_MASK		BIT(PFERR_SGX_BIT)
> -#define PFERR_GUEST_FINAL_MASK	BIT_ULL(PFERR_GUEST_FINAL_BIT)
> -#define PFERR_GUEST_PAGE_MASK	BIT_ULL(PFERR_GUEST_PAGE_BIT)
> -#define PFERR_IMPLICIT_ACCESS	BIT_ULL(PFERR_IMPLICIT_ACCESS_BIT)
> +#define PFERR_PRESENT_MASK	BIT(0)
> +#define PFERR_WRITE_MASK	BIT(1)
> +#define PFERR_USER_MASK		BIT(2)
> +#define PFERR_RSVD_MASK		BIT(3)
> +#define PFERR_FETCH_MASK	BIT(4)
> +#define PFERR_PK_MASK		BIT(5)
> +#define PFERR_SGX_MASK		BIT(15)
> +#define PFERR_GUEST_FINAL_MASK	BIT_ULL(32)
> +#define PFERR_GUEST_PAGE_MASK	BIT_ULL(33)
> +#define PFERR_IMPLICIT_ACCESS	BIT_ULL(48)
>  
>  #define PFERR_NESTED_GUEST_PAGE (PFERR_GUEST_PAGE_MASK |	\
>  				 PFERR_WRITE_MASK |		\
> diff --git a/arch/x86/kvm/mmu.h b/arch/x86/kvm/mmu.h
> index 60f21bb4c27b..e8b620a85627 100644
> --- a/arch/x86/kvm/mmu.h
> +++ b/arch/x86/kvm/mmu.h
> @@ -213,7 +213,7 @@ static inline u8 permission_fault(struct kvm_vcpu *vcpu, struct kvm_mmu *mmu,
>  	 */
>  	u64 implicit_access = access & PFERR_IMPLICIT_ACCESS;
>  	bool not_smap = ((rflags & X86_EFLAGS_AC) | implicit_access) == X86_EFLAGS_AC;
> -	int index = (pfec + (not_smap << PFERR_RSVD_BIT)) >> 1;
> +	int index = (pfec + (not_smap << ilog2(PFERR_RSVD_MASK))) >> 1;
>  	u32 errcode = PFERR_PRESENT_MASK;
>  	bool fault;
>  
> @@ -235,7 +235,7 @@ static inline u8 permission_fault(struct kvm_vcpu *vcpu, struct kvm_mmu *mmu,
>  
>  		/* clear present bit, replace PFEC.RSVD with ACC_USER_MASK. */
>  		offset = (pfec & ~1) +
> -			((pte_access & PT_USER_MASK) << (PFERR_RSVD_BIT - PT_USER_SHIFT));
> +			((pte_access & PT_USER_MASK) << (ilog2(PFERR_RSVD_MASK) - PT_USER_SHIFT));
>  
>  		pkru_bits &= mmu->pkru_mask >> offset;
>  		errcode |= -pkru_bits & PFERR_PK_MASK;