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Date: Thu, 16 Mar 2023 10:38:02 +0000
From: "Huang, Kai" <kai.huang@...el.com>
To: "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
"Yamahata, Isaku" <isaku.yamahata@...el.com>
CC: "zhi.wang.linux@...il.com" <zhi.wang.linux@...il.com>,
"pbonzini@...hat.com" <pbonzini@...hat.com>,
"Shahar, Sagi" <sagis@...gle.com>,
"Aktas, Erdem" <erdemaktas@...gle.com>,
"isaku.yamahata@...il.com" <isaku.yamahata@...il.com>,
"dmatlack@...gle.com" <dmatlack@...gle.com>,
"Christopherson,, Sean" <seanjc@...gle.com>
Subject: Re: [PATCH v13 057/113] KVM: TDX: MTRR: implement get_mt_mask() for
TDX
On Sun, 2023-03-12 at 10:56 -0700, isaku.yamahata@...el.com wrote:
> From: Isaku Yamahata <isaku.yamahata@...el.com>
>
> Because TDX virtualize cpuid[0x1].EDX[MTRR: bit 12] to fixed 1, guest TD
> thinks MTRR is supported. Although TDX supports only WB for private GPA,
> it's desirable to support MTRR for shared GPA. As guest access to MTRR
> MSRs causes #VE and KVM/x86 tracks the values of MTRR MSRs, the remining
> part is to implement get_mt_mask method for TDX for shared GPA.
>
> Pass around shared bit from kvm fault handler to get_mt_mask method so that
> it can determine if the gfn is shared or private.
>
I think we have an Xarray to query whether a given GFN is shared or private?
Can we use that?
> Implement get_mt_mask()
> following vmx case for shared GPA and return WB for private GPA.
> the existing vmx_get_mt_mask() can't be directly used as CPU state(CR0.CD)
> is protected. GFN passed to kvm_mtrr_check_gfn_range_consistency() should
> include shared bit.
>
> Suggested-by: Kai Huang <kai.huang@...el.com>
I am not sure what is suggested by me?
I thought what I suggested is we should have a dedicated patch to handle MTRR
for TDX putting all related things together.
> Signed-off-by: Isaku Yamahata <isaku.yamahata@...el.com>
> ---
> Changes from v11 to V12
> - Make common function for VMX and TDX
> - pass around shared bit from KVM fault handler to get_mt_mask method
> - updated commit message
> ---
> arch/x86/kvm/mmu/mmu.c | 7 ++++++-
> arch/x86/kvm/mmu/spte.c | 5 +++--
> arch/x86/kvm/mmu/spte.h | 2 +-
> arch/x86/kvm/vmx/common.h | 2 ++
> arch/x86/kvm/vmx/main.c | 11 ++++++++++-
> arch/x86/kvm/vmx/tdx.c | 17 +++++++++++++++++
> arch/x86/kvm/vmx/vmx.c | 5 +++--
> arch/x86/kvm/vmx/x86_ops.h | 2 ++
> 8 files changed, 44 insertions(+), 7 deletions(-)
>
> diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
> index 6074aa09cd87..fb858594cfec 100644
> --- a/arch/x86/kvm/mmu/mmu.c
> +++ b/arch/x86/kvm/mmu/mmu.c
> @@ -4569,7 +4569,12 @@ int kvm_tdp_page_fault(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault)
> if (shadow_memtype_mask && kvm_arch_has_noncoherent_dma(vcpu->kvm)) {
> for ( ; fault->max_level > PG_LEVEL_4K; --fault->max_level) {
> int page_num = KVM_PAGES_PER_HPAGE(fault->max_level);
> - gfn_t base = gfn_round_for_level(fault->gfn,
> + /*
> + * kvm_mtrr_check_gfn_range_consistency() requires gfn
> + * including shared bit.
>
Why? MTRR MSRs should always contain the true GFN without shared bit, correct?
Then why kvm_mtrr_check_gfn_range_consistency() needs shared bit?
> fault->gfn is masked out with
> + * shared bit. So fault->gfn can't be used.
> + */
> + gfn_t base = gfn_round_for_level(gpa_to_gfn(fault->addr),
> fault->max_level);
>
> if (kvm_mtrr_check_gfn_range_consistency(vcpu, base, page_num))
> diff --git a/arch/x86/kvm/mmu/spte.c b/arch/x86/kvm/mmu/spte.c
> index 180907ef26c7..7adb0d00ec4b 100644
> --- a/arch/x86/kvm/mmu/spte.c
> +++ b/arch/x86/kvm/mmu/spte.c
> @@ -137,13 +137,14 @@ bool spte_has_volatile_bits(u64 spte)
>
> bool make_spte(struct kvm_vcpu *vcpu, struct kvm_mmu_page *sp,
> const struct kvm_memory_slot *slot,
> - unsigned int pte_access, gfn_t gfn, kvm_pfn_t pfn,
> + unsigned int pte_access, gfn_t gfn_including_shared, kvm_pfn_t pfn,
IMHO 'gfn_including_shared' is ugly, especially changing from 'gfn' in _THIS_
particular patch.
> u64 old_spte, bool prefetch, bool can_unsync,
> bool host_writable, u64 *new_spte)
> {
> int level = sp->role.level;
> u64 spte = SPTE_MMU_PRESENT_MASK;
> bool wrprot = false;
> + gfn_t gfn = gfn_including_shared & ~kvm_gfn_shared_mask(vcpu->kvm);
>
> WARN_ON_ONCE(!pte_access && !shadow_present_mask);
>
> @@ -191,7 +192,7 @@ bool make_spte(struct kvm_vcpu *vcpu, struct kvm_mmu_page *sp,
> spte |= PT_PAGE_SIZE_MASK;
>
> if (shadow_memtype_mask)
> - spte |= static_call(kvm_x86_get_mt_mask)(vcpu, gfn,
> + spte |= static_call(kvm_x86_get_mt_mask)(vcpu, gfn_including_shared,
> kvm_is_mmio_pfn(pfn));
> if (host_writable)
> spte |= shadow_host_writable_mask;
> diff --git a/arch/x86/kvm/mmu/spte.h b/arch/x86/kvm/mmu/spte.h
> index 41973fe6bc22..62280c4b8c81 100644
> --- a/arch/x86/kvm/mmu/spte.h
> +++ b/arch/x86/kvm/mmu/spte.h
> @@ -481,7 +481,7 @@ bool spte_has_volatile_bits(u64 spte);
>
> bool make_spte(struct kvm_vcpu *vcpu, struct kvm_mmu_page *sp,
> const struct kvm_memory_slot *slot,
> - unsigned int pte_access, gfn_t gfn, kvm_pfn_t pfn,
> + unsigned int pte_access, gfn_t gfn_including_shared, kvm_pfn_t pfn,
> u64 old_spte, bool prefetch, bool can_unsync,
> bool host_writable, u64 *new_spte);
> u64 make_huge_page_split_spte(struct kvm *kvm, u64 huge_spte,
> diff --git a/arch/x86/kvm/vmx/common.h b/arch/x86/kvm/vmx/common.h
> index 235908f3e044..422b24af7fc1 100644
> --- a/arch/x86/kvm/vmx/common.h
> +++ b/arch/x86/kvm/vmx/common.h
> @@ -6,6 +6,8 @@
>
> #include "mmu.h"
>
> +u8 __vmx_get_mt_mask(struct kvm_vcpu *vcpu, gfn_t gfn, bool is_mmio, bool check_cr0_cd);
> +
> static inline int __vmx_handle_ept_violation(struct kvm_vcpu *vcpu, gpa_t gpa,
> unsigned long exit_qualification)
> {
> diff --git a/arch/x86/kvm/vmx/main.c b/arch/x86/kvm/vmx/main.c
> index 902b57506291..55001b34e1f0 100644
> --- a/arch/x86/kvm/vmx/main.c
> +++ b/arch/x86/kvm/vmx/main.c
> @@ -3,6 +3,7 @@
>
> #include "x86_ops.h"
> #include "mmu.h"
> +#include "common.h"
> #include "vmx.h"
> #include "nested.h"
> #include "mmu.h"
> @@ -228,6 +229,14 @@ static void vt_load_mmu_pgd(struct kvm_vcpu *vcpu, hpa_t root_hpa,
> vmx_load_mmu_pgd(vcpu, root_hpa, pgd_level);
> }
>
> +static u8 vt_get_mt_mask(struct kvm_vcpu *vcpu, gfn_t gfn, bool is_mmio)
> +{
> + if (is_td_vcpu(vcpu))
> + return tdx_get_mt_mask(vcpu, gfn, is_mmio);
> +
> + return __vmx_get_mt_mask(vcpu, gfn, is_mmio, true);
> +}
> +
> static int vt_mem_enc_ioctl(struct kvm *kvm, void __user *argp)
> {
> if (!is_td(kvm))
> @@ -348,7 +357,7 @@ struct kvm_x86_ops vt_x86_ops __initdata = {
>
> .set_tss_addr = vmx_set_tss_addr,
> .set_identity_map_addr = vmx_set_identity_map_addr,
> - .get_mt_mask = vmx_get_mt_mask,
> + .get_mt_mask = vt_get_mt_mask,
>
> .get_exit_info = vmx_get_exit_info,
>
> diff --git a/arch/x86/kvm/vmx/tdx.c b/arch/x86/kvm/vmx/tdx.c
> index 6ab7580de69c..b7b4ab60f96d 100644
> --- a/arch/x86/kvm/vmx/tdx.c
> +++ b/arch/x86/kvm/vmx/tdx.c
> @@ -5,6 +5,7 @@
>
> #include "capabilities.h"
> #include "x86_ops.h"
> +#include "common.h"
> #include "tdx.h"
> #include "vmx.h"
> #include "x86.h"
> @@ -350,6 +351,22 @@ int tdx_vm_init(struct kvm *kvm)
> return 0;
> }
>
> +u8 tdx_get_mt_mask(struct kvm_vcpu *vcpu, gfn_t gfn, bool is_mmio)
> +{
> + /* TDX private GPA is always WB. */
> + if (!(gfn & kvm_gfn_shared_mask(vcpu->kvm))) {
> + /* MMIO is only for shared GPA. */
> + WARN_ON_ONCE(is_mmio);
> + return MTRR_TYPE_WRBACK << VMX_EPT_MT_EPTE_SHIFT;
> + }
> +
> + /* Drop shared bit as MTRR doesn't know about shared bit. */
> + gfn = kvm_gfn_to_private(vcpu->kvm, gfn);
> +
> + /* As TDX enforces CR0.CD to 0, pass check_cr0_cd = false. */
> + return __vmx_get_mt_mask(vcpu, gfn, is_mmio, false);
> +}
Do you know whether there's any use case of non-coherent device assignment to
TDX guest?
IMHO, we should just disallow TDX guest to support non-coherent device
assignment, so that we can just return WB for both private and shared.
If we support non-coherent device assignment, then if guest sets private memory
to non-WB memory, it believes the memory type is non-WB, but in fact TDX always
map private memory as WB.
Will this be a problem, i.e. if assigned device can DMA to private memory
directly in the future?
> +
> int tdx_vcpu_create(struct kvm_vcpu *vcpu)
> {
> /*
> diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
> index 23321b2208ae..b8d8f7fbeb69 100644
> --- a/arch/x86/kvm/vmx/vmx.c
> +++ b/arch/x86/kvm/vmx/vmx.c
> @@ -7568,7 +7568,8 @@ int vmx_vm_init(struct kvm *kvm)
> return 0;
> }
>
> -u8 vmx_get_mt_mask(struct kvm_vcpu *vcpu, gfn_t gfn, bool is_mmio)
> +u8 __vmx_get_mt_mask(struct kvm_vcpu *vcpu, gfn_t gfn, bool is_mmio,
> + bool check_cr0_cd)
> {
> u8 cache;
>
> @@ -7596,7 +7597,7 @@ u8 vmx_get_mt_mask(struct kvm_vcpu *vcpu, gfn_t gfn, bool is_mmio)
> if (!kvm_arch_has_noncoherent_dma(vcpu->kvm))
> return (MTRR_TYPE_WRBACK << VMX_EPT_MT_EPTE_SHIFT) | VMX_EPT_IPAT_BIT;
>
> - if (kvm_read_cr0(vcpu) & X86_CR0_CD) {
> + if (check_cr0_cd && kvm_read_cr0(vcpu) & X86_CR0_CD) {
> if (kvm_check_has_quirk(vcpu->kvm, KVM_X86_QUIRK_CD_NW_CLEARED))
> cache = MTRR_TYPE_WRBACK;
> else
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