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

Binbin Wu
2023-11-20T10:54:18Z

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)