Re: [PATCH v6 07/16] KVM: MMU: Introduce level info in PFERR code

[Binbin Wu <binbin.wu@linux.intel.com>]

On 11/7/2023 11:00 PM, isaku.yamahata@intel.com wrote:
> From: Xiaoyao Li <xiaoyao.li@intel.com>
>
> For TDX, EPT violation can happen when TDG.MEM.PAGE.ACCEPT.
> And TDG.MEM.PAGE.ACCEPT contains the desired accept page level of TD guest.
>
> 1. KVM can map it with 4KB page while TD guest wants to accept 2MB page.
>
>    TD geust will get TDX_PAGE_SIZE_MISMATCH and it should try to accept
s/geust/guest

>    4KB size.
>
> 2. KVM can map it with 2MB page while TD guest wants to accept 4KB page.
>
>    KVM needs to honor it because
>    a) there is no way to tell guest KVM maps it as 2MB size. And
>    b) guest accepts it in 4KB size since guest knows some other 4KB page
>       in the same 2MB range will be used as shared page.
>
> For case 2, it need to pass desired page level to MMU's
> page_fault_handler. Use bit 29:31 of kvm PF error code for this purpose.

The level info is needed not only for case 2, KVM also needs the info so 
that
it can map a 2MB page when TD guest wants to accept a 2MB page.


>
> Signed-off-by: Xiaoyao Li <xiaoyao.li@intel.com>
> Signed-off-by: Isaku Yamahata <isaku.yamahata@intel.com>
> ---
>   arch/x86/include/asm/kvm_host.h |  3 +++
>   arch/x86/kvm/mmu/mmu.c          |  5 +++++
>   arch/x86/kvm/vmx/common.h       |  6 +++++-
>   arch/x86/kvm/vmx/tdx.c          | 15 ++++++++++++++-
>   arch/x86/kvm/vmx/tdx.h          | 19 +++++++++++++++++++
>   arch/x86/kvm/vmx/vmx.c          |  2 +-
>   6 files changed, 47 insertions(+), 3 deletions(-)
>
> diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
> index edcafcd650db..eed36c1eedb7 100644
> --- a/arch/x86/include/asm/kvm_host.h
> +++ b/arch/x86/include/asm/kvm_host.h
> @@ -261,6 +261,8 @@ enum x86_intercept_stage;
>   #define PFERR_FETCH_BIT 4
>   #define PFERR_PK_BIT 5
>   #define PFERR_SGX_BIT 15
> +#define PFERR_LEVEL_START_BIT 29
> +#define PFERR_LEVEL_END_BIT 31
>   #define PFERR_GUEST_FINAL_BIT 32
>   #define PFERR_GUEST_PAGE_BIT 33
>   #define PFERR_GUEST_ENC_BIT 34
> @@ -273,6 +275,7 @@ enum x86_intercept_stage;
>   #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_LEVEL_MASK	GENMASK_ULL(PFERR_LEVEL_END_BIT, PFERR_LEVEL_START_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_GUEST_ENC_MASK	BIT_ULL(PFERR_GUEST_ENC_BIT)
> diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
> index eb17a508c5d1..265177cedf37 100644
> --- a/arch/x86/kvm/mmu/mmu.c
> +++ b/arch/x86/kvm/mmu/mmu.c
> @@ -4615,6 +4615,11 @@ bool __kvm_mmu_honors_guest_mtrrs(bool vm_has_noncoherent_dma)
>   
>   int kvm_tdp_page_fault(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault)
>   {
> +	u8 err_level = (fault->error_code & PFERR_LEVEL_MASK) >> PFERR_LEVEL_START_BIT;
> +
> +	if (err_level)
> +		fault->max_level = min(fault->max_level, err_level);
> +
>   	/*
>   	 * If the guest's MTRRs may be used to compute the "real" memtype,
>   	 * restrict the mapping level to ensure KVM uses a consistent memtype
> diff --git a/arch/x86/kvm/vmx/common.h b/arch/x86/kvm/vmx/common.h
> index 027aa4175d2c..bb00433932ee 100644
> --- a/arch/x86/kvm/vmx/common.h
> +++ b/arch/x86/kvm/vmx/common.h
> @@ -67,7 +67,8 @@ static inline void vmx_handle_external_interrupt_irqoff(struct kvm_vcpu *vcpu,
>   }
>   
>   static inline int __vmx_handle_ept_violation(struct kvm_vcpu *vcpu, gpa_t gpa,
> -					     unsigned long exit_qualification)
> +					     unsigned long exit_qualification,
> +					     int err_page_level)
>   {
>   	u64 error_code;
>   
> @@ -90,6 +91,9 @@ static inline int __vmx_handle_ept_violation(struct kvm_vcpu *vcpu, gpa_t gpa,
>   	if (kvm_is_private_gpa(vcpu->kvm, gpa))
>   		error_code |= PFERR_GUEST_ENC_MASK;
>   
> +	if (err_page_level > 0)
> +		error_code |= (err_page_level << PFERR_LEVEL_START_BIT) & PFERR_LEVEL_MASK;
> +
>   	return kvm_mmu_page_fault(vcpu, gpa, error_code, NULL, 0);
>   }
>   
> diff --git a/arch/x86/kvm/vmx/tdx.c b/arch/x86/kvm/vmx/tdx.c
> index 31598b84811f..e4167f08b58b 100644
> --- a/arch/x86/kvm/vmx/tdx.c
> +++ b/arch/x86/kvm/vmx/tdx.c
> @@ -1803,7 +1803,20 @@ void tdx_deliver_interrupt(struct kvm_lapic *apic, int delivery_mode,
>   
>   static int tdx_handle_ept_violation(struct kvm_vcpu *vcpu)
>   {
> +	union tdx_ext_exit_qualification ext_exit_qual;
>   	unsigned long exit_qual;
> +	int err_page_level = 0;
> +
> +	ext_exit_qual.full = tdexit_ext_exit_qual(vcpu);
> +
> +	if (ext_exit_qual.type >= NUM_EXT_EXIT_QUAL) {
Can we add unlikely() hint here?

> +		pr_err("EPT violation at gpa 0x%lx, with invalid ext exit qualification type 0x%x\n",
> +			tdexit_gpa(vcpu), ext_exit_qual.type);
> +		kvm_vm_bugged(vcpu->kvm);
> +		return 0;
> +	} else if (ext_exit_qual.type == EXT_EXIT_QUAL_ACCEPT) {
> +		err_page_level = tdx_sept_level_to_pg_level(ext_exit_qual.req_sept_level);
> +	}
>   
>   	if (kvm_is_private_gpa(vcpu->kvm, tdexit_gpa(vcpu))) {
>   		/*
> @@ -1830,7 +1843,7 @@ static int tdx_handle_ept_violation(struct kvm_vcpu *vcpu)
>   	}
>   
>   	trace_kvm_page_fault(vcpu, tdexit_gpa(vcpu), exit_qual);
> -	return __vmx_handle_ept_violation(vcpu, tdexit_gpa(vcpu), exit_qual);
> +	return __vmx_handle_ept_violation(vcpu, tdexit_gpa(vcpu), exit_qual, err_page_level);
>   }
>   
>   static int tdx_handle_ept_misconfig(struct kvm_vcpu *vcpu)
> diff --git a/arch/x86/kvm/vmx/tdx.h b/arch/x86/kvm/vmx/tdx.h
> index 54c3f6b83571..37ee944c36a1 100644
> --- a/arch/x86/kvm/vmx/tdx.h
> +++ b/arch/x86/kvm/vmx/tdx.h
> @@ -72,6 +72,25 @@ union tdx_exit_reason {
>   	u64 full;
>   };
>   
> +union tdx_ext_exit_qualification {
> +	struct {
> +		u64 type		: 4;
> +		u64 reserved0		: 28;
> +		u64 req_sept_level	: 3;
> +		u64 err_sept_level	: 3;
> +		u64 err_sept_state	: 8;
> +		u64 err_sept_is_leaf	: 1;
> +		u64 reserved1		: 17;
> +	};
> +	u64 full;
> +};
> +
> +enum tdx_ext_exit_qualification_type {
> +	EXT_EXIT_QUAL_NONE,
> +	EXT_EXIT_QUAL_ACCEPT,
> +	NUM_EXT_EXIT_QUAL,
> +};
> +
>   struct vcpu_tdx {
>   	struct kvm_vcpu	vcpu;
>   
> diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
> index 28732925792e..ae9ba0731521 100644
> --- a/arch/x86/kvm/vmx/vmx.c
> +++ b/arch/x86/kvm/vmx/vmx.c
> @@ -5753,7 +5753,7 @@ static int handle_ept_violation(struct kvm_vcpu *vcpu)
>   	if (unlikely(allow_smaller_maxphyaddr && kvm_vcpu_is_illegal_gpa(vcpu, gpa)))
>   		return kvm_emulate_instruction(vcpu, 0);
>   
> -	return __vmx_handle_ept_violation(vcpu, gpa, exit_qualification);
> +	return __vmx_handle_ept_violation(vcpu, gpa, exit_qualification, 0);
>   }
>   
>   static int handle_ept_misconfig(struct kvm_vcpu *vcpu)