Re: [PATCH v7 037/102] KVM: x86/mmu: Track shadow MMIO value/mask on a per-VM basis

From: Kai Huang
Date: Tue Jul 19 2022 - 23:46:11 EST

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In reply to: Isaku Yamahata: "Re: [PATCH v7 037/102] KVM: x86/mmu: Track shadow MMIO value/mask on a per-VM basis"
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On Tue, 2022-07-19 at 01:47 -0700, Isaku Yamahata wrote:
> Here is the updated one. The changes are
> - removed hunks that should be a part of other patches.
> - removed shadow_default_mmio_mask
> - trimed down commit messages.
>
> From ed6b4a076e515550878b069596cf156a1bc33514 Mon Sep 17 00:00:00 2001
> Message-Id: <ed6b4a076e515550878b069596cf156a1bc33514.1658220363.git.isaku.yamahata@xxxxxxxxx>
> In-Reply-To: <3941849bf08a55cfbbe69b222f0fd0dac7c5ee53.1658220363.git.isaku.yamahata@xxxxxxxxx>
> References: <3941849bf08a55cfbbe69b222f0fd0dac7c5ee53.1658220363.git.isaku.yamahata@xxxxxxxxx>
> From: Sean Christopherson <sean.j.christopherson@xxxxxxxxx>
> Date: Wed, 10 Jun 2020 15:46:38 -0700
> Subject: [PATCH 036/306] KVM: x86/mmu: Track shadow MMIO value/mask on a
> per-VM basis
>
> TDX will use a different shadow PTE entry value for MMIO from VMX. Add
> members to kvm_arch and track value for MMIO per-VM instead of global
> variables. By using the per-VM EPT entry value for MMIO, the existing VMX
> logic is kept working. To untangle the logic to initialize
> shadow_mmio_access_mask, introduce a setter function.

introduce a separate setter function for it.

>
> Signed-off-by: Sean Christopherson <sean.j.christopherson@xxxxxxxxx>
> Signed-off-by: Isaku Yamahata <isaku.yamahata@xxxxxxxxx>
> ---
> arch/x86/include/asm/kvm_host.h | 4 +++
> arch/x86/kvm/mmu.h | 3 ++-
> arch/x86/kvm/mmu/mmu.c | 8 +++---
> arch/x86/kvm/mmu/spte.c | 45 +++++++++------------------------
> arch/x86/kvm/mmu/spte.h | 10 +++-----
> arch/x86/kvm/mmu/tdp_mmu.c | 6 ++---
> arch/x86/kvm/svm/svm.c | 11 +++++---
> arch/x86/kvm/vmx/tdx.c | 4 +++
> arch/x86/kvm/vmx/vmx.c | 26 +++++++++++++++++++
> arch/x86/kvm/vmx/x86_ops.h | 1 +
> 10 files changed, 66 insertions(+), 52 deletions(-)
>
> diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
> index 2c47aab72a1b..39215daa8576 100644
> --- a/arch/x86/include/asm/kvm_host.h
> +++ b/arch/x86/include/asm/kvm_host.h
> @@ -1161,6 +1161,10 @@ struct kvm_arch {
> */
> spinlock_t mmu_unsync_pages_lock;
>
> + bool enable_mmio_caching;
> + u64 shadow_mmio_value;
> + u64 shadow_mmio_mask;
> +
> struct list_head assigned_dev_head;
> struct iommu_domain *iommu_domain;
> bool iommu_noncoherent;
> diff --git a/arch/x86/kvm/mmu.h b/arch/x86/kvm/mmu.h
> index ccf0ba7a6387..cfa3e658162c 100644
> --- a/arch/x86/kvm/mmu.h
> +++ b/arch/x86/kvm/mmu.h
> @@ -108,7 +108,8 @@ static inline u8 kvm_get_shadow_phys_bits(void)
> return boot_cpu_data.x86_phys_bits;
> }
>
> -void kvm_mmu_set_mmio_spte_mask(u64 mmio_value, u64 mmio_mask, u64 access_mask);
> +void kvm_mmu_set_mmio_spte_mask(struct kvm *kvm, u64 mmio_value, u64 mmio_mask);
> +void kvm_mmu_set_mmio_access_mask(u64 mmio_access_mask);
> void kvm_mmu_set_me_spte_mask(u64 me_value, u64 me_mask);
> void kvm_mmu_set_ept_masks(bool has_ad_bits, bool has_exec_only);
>
> diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
> index 5bfccfa0f50e..34240fcc45de 100644
> --- a/arch/x86/kvm/mmu/mmu.c
> +++ b/arch/x86/kvm/mmu/mmu.c
> @@ -2298,7 +2298,7 @@ static int mmu_page_zap_pte(struct kvm *kvm, struct kvm_mmu_page *sp,
> return kvm_mmu_prepare_zap_page(kvm, child,
> invalid_list);
> }
> - } else if (is_mmio_spte(pte)) {
> + } else if (is_mmio_spte(kvm, pte)) {
> mmu_spte_clear_no_track(spte);
> }
> return 0;
> @@ -3079,7 +3079,7 @@ static int handle_abnormal_pfn(struct kvm_vcpu *vcpu, struct kvm_page_fault *fau
> * and only if L1's MAXPHYADDR is inaccurate with respect to
> * the hardware's).
> */
> - if (unlikely(!enable_mmio_caching) ||
> + if (unlikely(!vcpu->kvm->arch.enable_mmio_caching) ||
> unlikely(fault->gfn > kvm_mmu_max_gfn()))
> return RET_PF_EMULATE;
> }
> @@ -3918,7 +3918,7 @@ static int handle_mmio_page_fault(struct kvm_vcpu *vcpu, u64 addr, bool direct)
> if (WARN_ON(reserved))
> return -EINVAL;
>
> - if (is_mmio_spte(spte)) {
> + if (is_mmio_spte(vcpu->kvm, spte)) {
> gfn_t gfn = get_mmio_spte_gfn(spte);
> unsigned int access = get_mmio_spte_access(spte);
>
> @@ -4361,7 +4361,7 @@ static unsigned long get_cr3(struct kvm_vcpu *vcpu)
> static bool sync_mmio_spte(struct kvm_vcpu *vcpu, u64 *sptep, gfn_t gfn,
> unsigned int access)
> {
> - if (unlikely(is_mmio_spte(*sptep))) {
> + if (unlikely(is_mmio_spte(vcpu->kvm, *sptep))) {
> if (gfn != get_mmio_spte_gfn(*sptep)) {
> mmu_spte_clear_no_track(sptep);
> return true;
> diff --git a/arch/x86/kvm/mmu/spte.c b/arch/x86/kvm/mmu/spte.c
> index 92968e5605fc..9a130dd3d6a3 100644
> --- a/arch/x86/kvm/mmu/spte.c
> +++ b/arch/x86/kvm/mmu/spte.c
> @@ -29,8 +29,6 @@ u64 __read_mostly shadow_x_mask; /* mutual exclusive with nx_mask */
> u64 __read_mostly shadow_user_mask;
> u64 __read_mostly shadow_accessed_mask;
> u64 __read_mostly shadow_dirty_mask;
> -u64 __read_mostly shadow_mmio_value;
> -u64 __read_mostly shadow_mmio_mask;
> u64 __read_mostly shadow_mmio_access_mask;
> u64 __read_mostly shadow_present_mask;
> u64 __read_mostly shadow_me_value;
> @@ -62,10 +60,10 @@ u64 make_mmio_spte(struct kvm_vcpu *vcpu, u64 gfn, unsigned int access)
> u64 spte = generation_mmio_spte_mask(gen);
> u64 gpa = gfn << PAGE_SHIFT;
>
> - WARN_ON_ONCE(!shadow_mmio_value);
> + WARN_ON_ONCE(!vcpu->kvm->arch.shadow_mmio_value);
>
> access &= shadow_mmio_access_mask;
> - spte |= shadow_mmio_value | access;
> + spte |= vcpu->kvm->arch.shadow_mmio_value | access;
> spte |= gpa | shadow_nonpresent_or_rsvd_mask;
> spte |= (gpa & shadow_nonpresent_or_rsvd_mask)
> << SHADOW_NONPRESENT_OR_RSVD_MASK_LEN;
> @@ -337,9 +335,8 @@ u64 mark_spte_for_access_track(u64 spte)
> return spte;
> }
>
> -void kvm_mmu_set_mmio_spte_mask(u64 mmio_value, u64 mmio_mask, u64 access_mask)
> +void kvm_mmu_set_mmio_spte_mask(struct kvm *kvm, u64 mmio_value, u64 mmio_mask)
> {
> - BUG_ON((u64)(unsigned)access_mask != access_mask);
> WARN_ON(mmio_value & shadow_nonpresent_or_rsvd_lower_gfn_mask);
>
> if (!enable_mmio_caching)
> @@ -366,12 +363,9 @@ void kvm_mmu_set_mmio_spte_mask(u64 mmio_value, u64 mmio_mask, u64 access_mask)
> WARN_ON(mmio_value && (__REMOVED_SPTE & mmio_mask) == mmio_value))
> mmio_value = 0;
>
> - if (!mmio_value)
> - enable_mmio_caching = false;
> -
> - shadow_mmio_value = mmio_value;
> - shadow_mmio_mask = mmio_mask;
> - shadow_mmio_access_mask = access_mask;
> + kvm->arch.enable_mmio_caching = !!mmio_value;

KVM has a global enable_mmio_caching boolean, and I think we should honor it
here (in this patch) by doing below first:

if (enabling_mmio_caching)
mmio_value = 0;

For TD guest, the logic around enable_mmio_caching doesn't make sense anymore,
so perhaps we can later tweak it by doing something like:

/*
* Treat mmio_caching is false for TD guest, or true for it, depending
* on how you define it.
*/
if (kvm_gfn_shared_mask(kvm))
kvm->arch.enable_mmio_caching = false; /* or true? */
else {
if (!enable_mmio_caching)
mmio_value = 0;
kvm->arch.enable_mmio_caching = !!mmio_value;
}

> + kvm->arch.shadow_mmio_value = mmio_value;
> + kvm->arch.shadow_mmio_mask = mmio_mask;
> }
> EXPORT_SYMBOL_GPL(kvm_mmu_set_mmio_spte_mask);
>
> @@ -399,20 +393,12 @@ void kvm_mmu_set_ept_masks(bool has_ad_bits, bool has_exec_only)
> shadow_acc_track_mask = VMX_EPT_RWX_MASK;
> shadow_host_writable_mask = EPT_SPTE_HOST_WRITABLE;
> shadow_mmu_writable_mask = EPT_SPTE_MMU_WRITABLE;
> -
> - /*
> - * EPT Misconfigurations are generated if the value of bits 2:0
> - * of an EPT paging-structure entry is 110b (write/execute).
> - */
> - kvm_mmu_set_mmio_spte_mask(VMX_EPT_MISCONFIG_WX_VALUE,
> - VMX_EPT_RWX_MASK, 0);
> }
> EXPORT_SYMBOL_GPL(kvm_mmu_set_ept_masks);
>
> void kvm_mmu_reset_all_pte_masks(void)
> {
> u8 low_phys_bits;
> - u64 mask;
>
> shadow_phys_bits = kvm_get_shadow_phys_bits();
>
> @@ -452,18 +438,11 @@ void kvm_mmu_reset_all_pte_masks(void)
>
> shadow_host_writable_mask = DEFAULT_SPTE_HOST_WRITABLE;
> shadow_mmu_writable_mask = DEFAULT_SPTE_MMU_WRITABLE;
> +}
>
> - /*
> - * Set a reserved PA bit in MMIO SPTEs to generate page faults with
> - * PFEC.RSVD=1 on MMIO accesses. 64-bit PTEs (PAE, x86-64, and EPT
> - * paging) support a maximum of 52 bits of PA, i.e. if the CPU supports
> - * 52-bit physical addresses then there are no reserved PA bits in the
> - * PTEs and so the reserved PA approach must be disabled.
> - */
> - if (shadow_phys_bits < 52)
> - mask = BIT_ULL(51) | PT_PRESENT_MASK;
> - else
> - mask = 0;
> -
> - kvm_mmu_set_mmio_spte_mask(mask, mask, ACC_WRITE_MASK | ACC_USER_MASK);
> +void kvm_mmu_set_mmio_access_mask(u64 mmio_access_mask)
> +{
> + BUG_ON((u64)(unsigned)mmio_access_mask != mmio_access_mask);
> + shadow_mmio_access_mask = mmio_access_mask;
> }
> +EXPORT_SYMBOL(kvm_mmu_set_mmio_access_mask);
> diff --git a/arch/x86/kvm/mmu/spte.h b/arch/x86/kvm/mmu/spte.h
> index f5fd22f6bf5f..99bce92b596e 100644
> --- a/arch/x86/kvm/mmu/spte.h
> +++ b/arch/x86/kvm/mmu/spte.h
> @@ -5,8 +5,6 @@
>
> #include "mmu_internal.h"
>
> -extern bool __read_mostly enable_mmio_caching;
> -

Here you removed the ability to control enable_mmio_caching globally. It's not
something you stated to do in the changelog. Perhaps we should still keep it,
and enforce it in kvm_mmu_set_mmio_spte_mask() as commented above.

And in upstream KVM, it is a module parameter. What happens to it?

> /*
> * A MMU present SPTE is backed by actual memory and may or may not be present
> * in hardware. E.g. MMIO SPTEs are not considered present. Use bit 11, as it
> @@ -160,8 +158,6 @@ extern u64 __read_mostly shadow_x_mask; /* mutual exclusive with nx_mask */
> extern u64 __read_mostly shadow_user_mask;
> extern u64 __read_mostly shadow_accessed_mask;
> extern u64 __read_mostly shadow_dirty_mask;
> -extern u64 __read_mostly shadow_mmio_value;
> -extern u64 __read_mostly shadow_mmio_mask;
> extern u64 __read_mostly shadow_mmio_access_mask;
> extern u64 __read_mostly shadow_present_mask;
> extern u64 __read_mostly shadow_me_value;
> @@ -228,10 +224,10 @@ static inline bool is_removed_spte(u64 spte)
> */
> extern u64 __read_mostly shadow_nonpresent_or_rsvd_lower_gfn_mask;
>
> -static inline bool is_mmio_spte(u64 spte)
> +static inline bool is_mmio_spte(struct kvm *kvm, u64 spte)
> {
> - return (spte & shadow_mmio_mask) == shadow_mmio_value &&
> - likely(enable_mmio_caching);
> + return (spte & kvm->arch.shadow_mmio_mask) == kvm->arch.shadow_mmio_value &&
> + likely(kvm->arch.enable_mmio_caching);
> }
>
> static inline bool is_shadow_present_pte(u64 pte)
> diff --git a/arch/x86/kvm/mmu/tdp_mmu.c b/arch/x86/kvm/mmu/tdp_mmu.c
> index 2ca03ec3bf52..82f1bfac7ee6 100644
> --- a/arch/x86/kvm/mmu/tdp_mmu.c
> +++ b/arch/x86/kvm/mmu/tdp_mmu.c
> @@ -569,8 +569,8 @@ static void __handle_changed_spte(struct kvm *kvm, int as_id, gfn_t gfn,
> * impact the guest since both the former and current SPTEs
> * are nonpresent.
> */
> - if (WARN_ON(!is_mmio_spte(old_spte) &&
> - !is_mmio_spte(new_spte) &&
> + if (WARN_ON(!is_mmio_spte(kvm, old_spte) &&
> + !is_mmio_spte(kvm, new_spte) &&
> !is_removed_spte(new_spte)))
> pr_err("Unexpected SPTE change! Nonpresent SPTEs\n"
> "should not be replaced with another,\n"
> @@ -1108,7 +1108,7 @@ static int tdp_mmu_map_handle_target_level(struct kvm_vcpu *vcpu,
> }
>
> /* If a MMIO SPTE is installed, the MMIO will need to be emulated. */
> - if (unlikely(is_mmio_spte(new_spte))) {
> + if (unlikely(is_mmio_spte(vcpu->kvm, new_spte))) {
> vcpu->stat.pf_mmio_spte_created++;
> trace_mark_mmio_spte(rcu_dereference(iter->sptep), iter->gfn,
> new_spte);
> diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
> index f01821f48bfd..0f63257161a6 100644
> --- a/arch/x86/kvm/svm/svm.c
> +++ b/arch/x86/kvm/svm/svm.c
> @@ -198,6 +198,7 @@ module_param(dump_invalid_vmcb, bool, 0644);
> bool intercept_smi = true;
> module_param(intercept_smi, bool, 0444);
>
> +static u64 __read_mostly svm_shadow_mmio_mask;
>
> static bool svm_gp_erratum_intercept = true;
>
> @@ -4685,6 +4686,9 @@ static bool svm_is_vm_type_supported(unsigned long type)
>
> static int svm_vm_init(struct kvm *kvm)
> {
> + kvm_mmu_set_mmio_spte_mask(kvm, svm_shadow_mmio_mask,
> + svm_shadow_mmio_mask);
> +
> if (!pause_filter_count || !pause_filter_thresh)
> kvm->arch.pause_in_guest = true;
>
> @@ -4834,7 +4838,7 @@ static struct kvm_x86_ops svm_x86_ops __initdata = {
> static __init void svm_adjust_mmio_mask(void)
> {
> unsigned int enc_bit, mask_bit;
> - u64 msr, mask;
> + u64 msr;
>
> /* If there is no memory encryption support, use existing mask */
> if (cpuid_eax(0x80000000) < 0x8000001f)
> @@ -4861,9 +4865,8 @@ static __init void svm_adjust_mmio_mask(void)
> *
> * If the mask bit location is 52 (or above), then clear the mask.
> */
> - mask = (mask_bit < 52) ? rsvd_bits(mask_bit, 51) | PT_PRESENT_MASK : 0;
> -
> - kvm_mmu_set_mmio_spte_mask(mask, mask, PT_WRITABLE_MASK | PT_USER_MASK);
> + svm_shadow_mmio_mask = (mask_bit < 52) ? rsvd_bits(mask_bit, 51) | PT_PRESENT_MASK : 0;
> + kvm_mmu_set_mmio_access_mask(PT_WRITABLE_MASK | PT_USER_MASK);
> }
>
> static __init void svm_set_cpu_caps(void)
> diff --git a/arch/x86/kvm/vmx/tdx.c b/arch/x86/kvm/vmx/tdx.c
> index 36d2127cb7b7..52fb54880f9b 100644
> --- a/arch/x86/kvm/vmx/tdx.c
> +++ b/arch/x86/kvm/vmx/tdx.c
> @@ -7,6 +7,7 @@
> #include "x86_ops.h"
> #include "tdx.h"
> #include "x86.h"
> +#include "mmu.h"
>
> #undef pr_fmt
> #define pr_fmt(fmt) "tdx: " fmt
> @@ -276,6 +277,9 @@ int tdx_vm_init(struct kvm *kvm)
> int ret, i;
> u64 err;
>
> + kvm_mmu_set_mmio_spte_mask(kvm, vmx_shadow_mmio_mask,
> + vmx_shadow_mmio_mask);
> +

I prefer to split this chunk out to another patch so this patch can be purely
infrastructural. In this way you can even move this patch around easily in
this series.

> /* vCPUs can't be created until after KVM_TDX_INIT_VM. */
> kvm->max_vcpus = 0;
>
> diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
> index e129ee663498..88e893fdffe8 100644
> --- a/arch/x86/kvm/vmx/vmx.c
> +++ b/arch/x86/kvm/vmx/vmx.c
> @@ -141,6 +141,8 @@ module_param_named(preemption_timer, enable_preemption_timer, bool, S_IRUGO);
> extern bool __read_mostly allow_smaller_maxphyaddr;
> module_param(allow_smaller_maxphyaddr, bool, S_IRUGO);
>
> +u64 __ro_after_init vmx_shadow_mmio_mask;
> +
> #define KVM_VM_CR0_ALWAYS_OFF (X86_CR0_NW | X86_CR0_CD)
> #define KVM_VM_CR0_ALWAYS_ON_UNRESTRICTED_GUEST X86_CR0_NE
> #define KVM_VM_CR0_ALWAYS_ON \
> @@ -7359,6 +7361,17 @@ int vmx_vm_init(struct kvm *kvm)
> if (!ple_gap)
> kvm->arch.pause_in_guest = true;
>
> + /*
> + * EPT Misconfigurations can be generated if the value of bits 2:0
> + * of an EPT paging-structure entry is 110b (write/execute).
> + */
> + if (enable_ept)
> + kvm_mmu_set_mmio_spte_mask(kvm, VMX_EPT_MISCONFIG_WX_VALUE,
> + VMX_EPT_RWX_MASK);
> + else
> + kvm_mmu_set_mmio_spte_mask(kvm, vmx_shadow_mmio_mask,
> + vmx_shadow_mmio_mask);
> +
> if (boot_cpu_has(X86_BUG_L1TF) && enable_ept) {
> switch (l1tf_mitigation) {
> case L1TF_MITIGATION_OFF:
> @@ -8358,6 +8371,19 @@ int __init vmx_init(void)
> if (!enable_ept)
> allow_smaller_maxphyaddr = true;
>
> + /*
> + * Set a reserved PA bit in MMIO SPTEs to generate page faults with
> + * PFEC.RSVD=1 on MMIO accesses. 64-bit PTEs (PAE, x86-64, and EPT
> + * paging) support a maximum of 52 bits of PA, i.e. if the CPU supports
> + * 52-bit physical addresses then there are no reserved PA bits in the
> + * PTEs and so the reserved PA approach must be disabled.
> + */
> + if (kvm_get_shadow_phys_bits() < 52)
> + vmx_shadow_mmio_mask = BIT_ULL(51) | PT_PRESENT_MASK;
> + else
> + vmx_shadow_mmio_mask = 0;
> + kvm_mmu_set_mmio_access_mask(0);
> +
> return 0;
> }
>
> diff --git a/arch/x86/kvm/vmx/x86_ops.h b/arch/x86/kvm/vmx/x86_ops.h
> index 7e38c7b756d4..279e5360c555 100644
> --- a/arch/x86/kvm/vmx/x86_ops.h
> +++ b/arch/x86/kvm/vmx/x86_ops.h
> @@ -13,6 +13,7 @@ void hv_vp_assist_page_exit(void);
> void __init vmx_init_early(void);
> int __init vmx_init(void);
> void vmx_exit(void);
> +extern u64 __ro_after_init vmx_shadow_mmio_mask;
>
> __init int vmx_cpu_has_kvm_support(void);
> __init int vmx_disabled_by_bios(void);
> --
> 2.25.1
>
>

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In reply to: Isaku Yamahata: "Re: [PATCH v7 037/102] KVM: x86/mmu: Track shadow MMIO value/mask on a per-VM basis"
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