linux-kernel - Re: [PATCH 04/16] KVM: x86/mmu: Pass full 64-bit error code when handling page faults

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Message-ID: <6c10e17a-b1f2-c587-fbdd-85d15256b507@oracle.com>
Date: Tue, 27 Feb 2024 23:30:32 -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 04/16] KVM: x86/mmu: Pass full 64-bit error code when
 handling page faults



On 2/27/24 18:41, Sean Christopherson wrote:
> From: Isaku Yamahata <isaku.yamahata@...el.com>
> 
> Plumb the full 64-bit error code throughout the page fault handling code
> so that KVM can use the upper 32 bits, e.g. SNP's PFERR_GUEST_ENC_MASK
> will be used to determine whether or not a fault is private vs. shared.
> 
> Note, passing the 64-bit error code to FNAME(walk_addr)() does NOT change
> the behavior of permission_fault() when invoked in the page fault path, as
> KVM explicitly clears PFERR_IMPLICIT_ACCESS in kvm_mmu_page_fault().

May this lead to a WARN_ON_ONCE?

5843 int noinline kvm_mmu_page_fault(struct kvm_vcpu *vcpu, gpa_t cr2_or_gpa,
u64 error_code,
5844                        void *insn, int insn_len)
5845 {
.. ...
5856          */
5857         if (WARN_ON_ONCE(error_code & PFERR_IMPLICIT_ACCESS))
5858                 error_code &= ~PFERR_IMPLICIT_ACCESS;

> 
> Continue passing '0' from the async #PF worker, as guest_memfd() and thus

:s/guest_memfd()/guest_memfd/ ?

Dongli Zhang



> private memory doesn't support async page faults.
> 
> Signed-off-by: Isaku Yamahata <isaku.yamahata@...el.com>
> [mdr: drop references/changes on rebase, update commit message]
> Signed-off-by: Michael Roth <michael.roth@....com>
> [sean: drop truncation in call to FNAME(walk_addr)(), rewrite changelog]
> Signed-off-by: Sean Christopherson <seanjc@...gle.com>
> ---
>  arch/x86/kvm/mmu/mmu.c          | 3 +--
>  arch/x86/kvm/mmu/mmu_internal.h | 4 ++--
>  arch/x86/kvm/mmu/mmutrace.h     | 2 +-
>  3 files changed, 4 insertions(+), 5 deletions(-)
> 
> diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
> index e2fd74e06ff8..408969ac1291 100644
> --- a/arch/x86/kvm/mmu/mmu.c
> +++ b/arch/x86/kvm/mmu/mmu.c
> @@ -5860,8 +5860,7 @@ int noinline kvm_mmu_page_fault(struct kvm_vcpu *vcpu, gpa_t cr2_or_gpa, u64 err
>  	}
>  
>  	if (r == RET_PF_INVALID) {
> -		r = kvm_mmu_do_page_fault(vcpu, cr2_or_gpa,
> -					  lower_32_bits(error_code), false,
> +		r = kvm_mmu_do_page_fault(vcpu, cr2_or_gpa, error_code, false,
>  					  &emulation_type);
>  		if (KVM_BUG_ON(r == RET_PF_INVALID, vcpu->kvm))
>  			return -EIO;
> diff --git a/arch/x86/kvm/mmu/mmu_internal.h b/arch/x86/kvm/mmu/mmu_internal.h
> index 0eea6c5a824d..1fab1f2359b5 100644
> --- a/arch/x86/kvm/mmu/mmu_internal.h
> +++ b/arch/x86/kvm/mmu/mmu_internal.h
> @@ -190,7 +190,7 @@ static inline bool is_nx_huge_page_enabled(struct kvm *kvm)
>  struct kvm_page_fault {
>  	/* arguments to kvm_mmu_do_page_fault.  */
>  	const gpa_t addr;
> -	const u32 error_code;
> +	const u64 error_code;
>  	const bool prefetch;
>  
>  	/* Derived from error_code.  */
> @@ -288,7 +288,7 @@ static inline void kvm_mmu_prepare_memory_fault_exit(struct kvm_vcpu *vcpu,
>  }
>  
>  static inline int kvm_mmu_do_page_fault(struct kvm_vcpu *vcpu, gpa_t cr2_or_gpa,
> -					u32 err, bool prefetch, int *emulation_type)
> +					u64 err, bool prefetch, int *emulation_type)
>  {
>  	struct kvm_page_fault fault = {
>  		.addr = cr2_or_gpa,
> diff --git a/arch/x86/kvm/mmu/mmutrace.h b/arch/x86/kvm/mmu/mmutrace.h
> index ae86820cef69..195d98bc8de8 100644
> --- a/arch/x86/kvm/mmu/mmutrace.h
> +++ b/arch/x86/kvm/mmu/mmutrace.h
> @@ -260,7 +260,7 @@ TRACE_EVENT(
>  	TP_STRUCT__entry(
>  		__field(int, vcpu_id)
>  		__field(gpa_t, cr2_or_gpa)
> -		__field(u32, error_code)
> +		__field(u64, error_code)
>  		__field(u64 *, sptep)
>  		__field(u64, old_spte)
>  		__field(u64, new_spte)