On Thu, Sep 02, 2021, Sean Christopherson wrote:
> On Tue, Aug 24, 2021, Lai Jiangshan wrote:
> Rather than force the sync here, what about kicking all vCPUs and retrying the
> page fault? The only gross part is that kvm_mmu_get_page() can now fail :-(
>
> ---
> arch/x86/include/asm/kvm_host.h | 3 ++-
> arch/x86/kvm/mmu/mmu.c | 9 +++++++--
> arch/x86/kvm/mmu/paging_tmpl.h | 4 ++++
> 3 files changed, 13 insertions(+), 3 deletions(-)
>
> diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
> index 09b256db394a..332b9fb3454c 100644
> --- a/arch/x86/include/asm/kvm_host.h
> +++ b/arch/x86/include/asm/kvm_host.h
> @@ -57,7 +57,8 @@
> #define KVM_REQ_MIGRATE_TIMER KVM_ARCH_REQ(0)
> #define KVM_REQ_REPORT_TPR_ACCESS KVM_ARCH_REQ(1)
> #define KVM_REQ_TRIPLE_FAULT KVM_ARCH_REQ(2)
> -#define KVM_REQ_MMU_SYNC KVM_ARCH_REQ(3)
> +#define KVM_REQ_MMU_SYNC \
> + KVM_ARCH_REQ_FLAGS(3, KVM_REQUEST_WAIT | KVM_REQUEST_NO_WAKEUP)
> #define KVM_REQ_CLOCK_UPDATE KVM_ARCH_REQ(4)
> #define KVM_REQ_LOAD_MMU_PGD KVM_ARCH_REQ(5)
> #define KVM_REQ_EVENT KVM_ARCH_REQ(6)
> diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
> index 4853c033e6ce..03293cd3c7ae 100644
> --- a/arch/x86/kvm/mmu/mmu.c
> +++ b/arch/x86/kvm/mmu/mmu.c
> @@ -2143,8 +2143,10 @@ static struct kvm_mmu_page *kvm_mmu_get_page(struct kvm_vcpu *vcpu,
> kvm_make_request(KVM_REQ_TLB_FLUSH_CURRENT, vcpu);
> }
>
> - if (sp->unsync_children)
> - kvm_make_request(KVM_REQ_MMU_SYNC, vcpu);
> + if (sp->unsync_children) {
> + kvm_make_all_cpus_request(KVM_REQ_MMU_SYNC, vcpu);
> + return NULL;
> + }
>
> __clear_sp_write_flooding_count(sp);
>
> @@ -2999,6 +3001,7 @@ static int __direct_map(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault)
>
> sp = kvm_mmu_get_page(vcpu, base_gfn, it.addr,
> it.level - 1, true, ACC_ALL);
> + BUG_ON(!sp);
>
> link_shadow_page(vcpu, it.sptep, sp);
> if (fault->is_tdp && fault->huge_page_disallowed &&
> @@ -3383,6 +3386,8 @@ static hpa_t mmu_alloc_root(struct kvm_vcpu *vcpu, gfn_t gfn, gva_t gva,
> struct kvm_mmu_page *sp;
>
> sp = kvm_mmu_get_page(vcpu, gfn, gva, level, direct, ACC_ALL);
> + BUG_ON(!sp);
Gah, this is obviously wrong when allocating an indirect root. On the happy side,
it points out a cleaner approach. I think this is what we want?
---
arch/x86/kvm/mmu/mmu.c | 3 ---
arch/x86/kvm/mmu/paging_tmpl.h | 4 ++++
2 files changed, 4 insertions(+), 3 deletions(-)
diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
index 4853c033e6ce..f24e8088192c 100644
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -2143,9 +2143,6 @@ static struct kvm_mmu_page *kvm_mmu_get_page(struct kvm_vcpu *vcpu,
kvm_make_request(KVM_REQ_TLB_FLUSH_CURRENT, vcpu);
}
- if (sp->unsync_children)
- kvm_make_request(KVM_REQ_MMU_SYNC, vcpu);
-
__clear_sp_write_flooding_count(sp);
trace_get_page:
diff --git a/arch/x86/kvm/mmu/paging_tmpl.h b/arch/x86/kvm/mmu/paging_tmpl.h
index 50ade6450ace..5b13918a55c2 100644
--- a/arch/x86/kvm/mmu/paging_tmpl.h
+++ b/arch/x86/kvm/mmu/paging_tmpl.h
@@ -704,6 +704,10 @@ static int FNAME(fetch)(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault,
access = gw->pt_access[it.level - 2];
sp = kvm_mmu_get_page(vcpu, table_gfn, fault->addr,
it.level-1, false, access);
+ if (sp->unsync_children) {
+ kvm_make_all_cpus_request(KVM_REQ_MMU_SYNC, vcpu);
+ return RET_PF_RETRY;
+ }
}
/*
--
