| Message ID | 20240501085210.2213060-14-michael.roth@amd.com |
|---|---|
| State | New |
| Headers | show |
| Series | Add AMD Secure Nested Paging (SEV-SNP) Hypervisor Support | expand |
On Wed, 2024-05-01 at 03:52 -0500, Michael Roth wrote: > This will handle the RMP table updates needed to put a page into a > private state before mapping it into an SEV-SNP guest. > > [...] > +int sev_gmem_prepare(struct kvm *kvm, kvm_pfn_t pfn, gfn_t gfn, int max_order) > +{ > + struct kvm_sev_info *sev = &to_kvm_svm(kvm)->sev_info; > + kvm_pfn_t pfn_aligned; > + gfn_t gfn_aligned; > + int level, rc; > + bool assigned; > + > + if (!sev_snp_guest(kvm)) > + return 0; > + > + rc = snp_lookup_rmpentry(pfn, &assigned, &level); > + if (rc) { > + pr_err_ratelimited("SEV: Failed to look up RMP entry: GFN %llx PFN %llx error %d\n", > + gfn, pfn, rc); > + return -ENOENT; > + } > + > + if (assigned) { > + pr_debug("%s: already assigned: gfn %llx pfn %llx max_order %d level %d\n", > + __func__, gfn, pfn, max_order, level); > + return 0; > + } > + > + if (is_large_rmp_possible(kvm, pfn, max_order)) { > + level = PG_LEVEL_2M; > + pfn_aligned = ALIGN_DOWN(pfn, PTRS_PER_PMD); > + gfn_aligned = ALIGN_DOWN(gfn, PTRS_PER_PMD); > + } else { > + level = PG_LEVEL_4K; > + pfn_aligned = pfn; > + gfn_aligned = gfn; > + } > + > + rc = rmp_make_private(pfn_aligned, gfn_to_gpa(gfn_aligned), level, sev->asid, false); > + if (rc) { > + pr_err_ratelimited("SEV: Failed to update RMP entry: GFN %llx PFN %llx level %d error %d\n", > + gfn, pfn, level, rc); > + return -EINVAL; > + } > + > + pr_debug("%s: updated: gfn %llx pfn %llx pfn_aligned %llx max_order %d level %d\n", > + __func__, gfn, pfn, pfn_aligned, max_order, level); > + > + return 0; > +} > diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c > index b70556608e8d..60783e9f2ae8 100644 > --- a/arch/x86/kvm/svm/svm.c > +++ b/arch/x86/kvm/svm/svm.c > @@ -5085,6 +5085,8 @@ static struct kvm_x86_ops svm_x86_ops __initdata = { > .vcpu_deliver_sipi_vector = svm_vcpu_deliver_sipi_vector, > .vcpu_get_apicv_inhibit_reasons = avic_vcpu_get_apicv_inhibit_reasons, > .alloc_apic_backing_page = svm_alloc_apic_backing_page, > + > + .gmem_prepare = sev_gmem_prepare, > }; > > +Rick, Isaku, I am wondering whether this can be done in the KVM page fault handler? The reason that I am asking is KVM will introduce several new kvm_x86_ops::xx_private_spte() ops for TDX to handle setting up the private mapping, and I am wondering whether SNP can just reuse some of them so we can avoid having this .gmem_prepare(): /* Add a page as page table page into private page table */ int (*link_private_spt)(struct kvm *kvm, gfn_t gfn, enum pg_level level, void *private_spt); /* * Free a page table page of private page table. * ... */ int (*free_private_spt)(struct kvm *kvm, gfn_t gfn, enum pg_level level, void *private_spt); /* Add a guest private page into private page table */ int (*set_private_spte)(struct kvm *kvm, gfn_t gfn, enum pg_level level, kvm_pfn_t pfn); /* Remove a guest private page from private page table*/ int (*remove_private_spte)(struct kvm *kvm, gfn_t gfn, enum pg_level level, kvm_pfn_t pfn); /* * Keep a guest private page mapped in private page table, * but clear its present bit */ int (*zap_private_spte)(struct kvm *kvm, gfn_t gfn, enum pg_level level); The idea behind these is in the fault handler: bool use_private_pt = fault->is_private && kvm_use_private_pt(kvm); root_pt = use_private_pt ? mmu->private_root_hpa : mmu->root_hpa; tdp_mmu_for_each_pte(&iter, root_pt, gfn, gfn+1, ..) { if (use_private_pt) kvm_x86_ops->xx_private_spte(); else // normal TDP MMU ops } Which means: if the fault is for private GPA, _AND_ when the VM has a separate private table, use the specific xx_private_spte() ops to handle private mapping. But I am thinking we can use those hooks for SNP too, because "conceptually", SNP also has concept of "private GPA" and must at least issue some command to update the RMP table when private mapping is setup/torn down. So if we change the above logic to use fault->is_private, but not 'use_private_pt' to decide whether to invoke the kvm_x86_ops::xx_private_spte(), then we can also implement SNP commands in those callbacks IIUC: if (fault->is_private && kvm_x86_ops::xx_private_spte()) kvm_x86_ops::xx_private_spte(); else // normal TDP MMU operation For SNP, these callbacks will operate on normal page table using the normal TDP MMU code, but can do additional things like issuing commands as shown in this patch. My understanding is SNP doesn't need specific handling for middle level page table, but should be able to utilize the ops when setting up / tearing down the leaf SPTE?
On Mon, May 20, 2024, Kai Huang wrote: > On Wed, 2024-05-01 at 03:52 -0500, Michael Roth wrote: > > This will handle the RMP table updates needed to put a page into a > > private state before mapping it into an SEV-SNP guest. > > > > > > [...] > > > +int sev_gmem_prepare(struct kvm *kvm, kvm_pfn_t pfn, gfn_t gfn, int max_order) ... > +Rick, Isaku, > > I am wondering whether this can be done in the KVM page fault handler? No, because the state of a pfn in the RMP is tied to the guest_memfd inode, not to the file descriptor, i.e. not to an individual VM. And the NPT page tables are treated as ephemeral for SNP.
On Mon, May 20, 2024 at 10:16:54AM +0000, "Huang, Kai" <kai.huang@intel.com> wrote: > On Wed, 2024-05-01 at 03:52 -0500, Michael Roth wrote: > > This will handle the RMP table updates needed to put a page into a > > private state before mapping it into an SEV-SNP guest. > > > > > > [...] > > > +int sev_gmem_prepare(struct kvm *kvm, kvm_pfn_t pfn, gfn_t gfn, int max_order) > > +{ > > + struct kvm_sev_info *sev = &to_kvm_svm(kvm)->sev_info; > > + kvm_pfn_t pfn_aligned; > > + gfn_t gfn_aligned; > > + int level, rc; > > + bool assigned; > > + > > + if (!sev_snp_guest(kvm)) > > + return 0; > > + > > + rc = snp_lookup_rmpentry(pfn, &assigned, &level); > > + if (rc) { > > + pr_err_ratelimited("SEV: Failed to look up RMP entry: GFN %llx PFN %llx error %d\n", > > + gfn, pfn, rc); > > + return -ENOENT; > > + } > > + > > + if (assigned) { > > + pr_debug("%s: already assigned: gfn %llx pfn %llx max_order %d level %d\n", > > + __func__, gfn, pfn, max_order, level); > > + return 0; > > + } > > + > > + if (is_large_rmp_possible(kvm, pfn, max_order)) { > > + level = PG_LEVEL_2M; > > + pfn_aligned = ALIGN_DOWN(pfn, PTRS_PER_PMD); > > + gfn_aligned = ALIGN_DOWN(gfn, PTRS_PER_PMD); > > + } else { > > + level = PG_LEVEL_4K; > > + pfn_aligned = pfn; > > + gfn_aligned = gfn; > > + } > > + > > + rc = rmp_make_private(pfn_aligned, gfn_to_gpa(gfn_aligned), level, sev->asid, false); > > + if (rc) { > > + pr_err_ratelimited("SEV: Failed to update RMP entry: GFN %llx PFN %llx level %d error %d\n", > > + gfn, pfn, level, rc); > > + return -EINVAL; > > + } > > + > > + pr_debug("%s: updated: gfn %llx pfn %llx pfn_aligned %llx max_order %d level %d\n", > > + __func__, gfn, pfn, pfn_aligned, max_order, level); > > + > > + return 0; > > +} > > diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c > > index b70556608e8d..60783e9f2ae8 100644 > > --- a/arch/x86/kvm/svm/svm.c > > +++ b/arch/x86/kvm/svm/svm.c > > @@ -5085,6 +5085,8 @@ static struct kvm_x86_ops svm_x86_ops __initdata = { > > .vcpu_deliver_sipi_vector = svm_vcpu_deliver_sipi_vector, > > .vcpu_get_apicv_inhibit_reasons = avic_vcpu_get_apicv_inhibit_reasons, > > .alloc_apic_backing_page = svm_alloc_apic_backing_page, > > + > > + .gmem_prepare = sev_gmem_prepare, > > }; > > > > > > +Rick, Isaku, > > I am wondering whether this can be done in the KVM page fault handler? > > The reason that I am asking is KVM will introduce several new > kvm_x86_ops::xx_private_spte() ops for TDX to handle setting up the > private mapping, and I am wondering whether SNP can just reuse some of > them so we can avoid having this .gmem_prepare(): Although I can't speak for SNP folks, I guess those hooks doesn't make sense for them. I guess they want to stay away from directly modifying the TDP MMU to add hooks to the TDP MMU. Instead, They intentionally chose to add hooks to guest_memfd. Maybe it's possible for SNP to use those hooks, what's the benefit for SNP? If you're looking for the benefit to allow the hooks of the TDP MMU for shared page table, what about other vm type? SW_PROTECTED or future one?
On 21/05/2024 5:35 am, Sean Christopherson wrote: > On Mon, May 20, 2024, Kai Huang wrote: >> On Wed, 2024-05-01 at 03:52 -0500, Michael Roth wrote: >>> This will handle the RMP table updates needed to put a page into a >>> private state before mapping it into an SEV-SNP guest. >>> >>> >> >> [...] >> >>> +int sev_gmem_prepare(struct kvm *kvm, kvm_pfn_t pfn, gfn_t gfn, int max_order) > > ... > >> +Rick, Isaku, >> >> I am wondering whether this can be done in the KVM page fault handler? > > No, because the state of a pfn in the RMP is tied to the guest_memfd inode, not > to the file descriptor, i.e. not to an individual VM. It's strange that as state of a PFN of SNP doesn't bind to individual VM, at least for the private pages. The command rpm_make_private() indeed reflects the mapping between PFN <-> <GFN, SSID>. rc = rmp_make_private(pfn_aligned, gfn_to_gpa(gfn_aligned), level, sev->asid, false); > And the NPT page tables > are treated as ephemeral for SNP. > Do you mean private mappings for SNP guest can be zapped from the VM (the private pages are still there unchanged) and re-mapped later w/o needing to have guest's explicit acceptance? If so, I think "we can zap" doesn't mean "we need to zap"? Because the privates are now pinned anyway. If we truly want to zap private mappings for SNP, IIUC it can be done by distinguishing whether a VM needs to use a separate private table, which is TDX-only. I'll look into the SNP spec to understand more.
On 21/05/2024 11:15 am, Sean Christopherson wrote: > On Tue, May 21, 2024, Kai Huang wrote: >> On 21/05/2024 5:35 am, Sean Christopherson wrote: >>> On Mon, May 20, 2024, Kai Huang wrote: >>>> I am wondering whether this can be done in the KVM page fault handler? >>> >>> No, because the state of a pfn in the RMP is tied to the guest_memfd inode, >>> not to the file descriptor, i.e. not to an individual VM. >> >> It's strange that as state of a PFN of SNP doesn't bind to individual VM, at >> least for the private pages. The command rpm_make_private() indeed reflects >> the mapping between PFN <-> <GFN, SSID>. > > s/SSID/ASID > > KVM allows a single ASID to be bound to multiple "struct kvm" instances, e.g. > for intra-host migration. If/when trusted I/O is a thing, presumably KVM will > also need to share the ASID with other entities, e.g. IOMMUFD. But is this the case for SNP? I thought due to the nature of private pages, they cannot be shared between VMs? So to me this RMP entry mapping for PFN <-> GFN for private page should just be per-VM. > >> rc = rmp_make_private(pfn_aligned, gfn_to_gpa(gfn_aligned), >> level, sev->asid, false); >> >>> And the NPT page tables are treated as ephemeral for SNP. >> >> Do you mean private mappings for SNP guest can be zapped from the VM (the >> private pages are still there unchanged) and re-mapped later w/o needing to >> have guest's explicit acceptance? > > Correct. > >> If so, I think "we can zap" doesn't mean "we need to zap"? > > Correct. > >> Because the privates are now pinned anyway. > > Pinning is an orthogonal issue. And it's not so much that the pfns are pinned > as it is that guest_memfd simply doesn't support page migration or swap at this > time. Yes. > > Regardless of whether or not guest_memfd supports page migration, KVM needs to > track the state of the physical page in guest_memfd, e.g. if it's been assigned > to the ASID versus if it's still in a shared state. I am not certain this can impact whether we want to do RMP commands via guest_memfd() hooks or TDP MMU hooks? > >> If we truly want to zap private mappings for SNP, IIUC it can be done by >> distinguishing whether a VM needs to use a separate private table, which is >> TDX-only. > > I wouldn't say we "want" to zap private mappings for SNP, rather that it's a lot > less work to keep KVM's existing behavior (literally do nothing) than it is to > rework the MMU and whatnot to not zap SPTEs. My thinking too. > And there's no big motivation to > avoid zapping because SNP VMs are unlikely to delete memslots. I think we should also consider MMU notifier? > > If it turns out that it's easy to preserve SNP mappings after TDX lands, then we > can certainly go that route, but AFAIK there's no reason to force the issue. No I am certainly not saying we should do SNP after TDX. Sorry I didn't closely monitor the status of this SNP patchset. My intention is just wanting to make the TDP MMU common code change more useful (since we need that for TDX anyway), i.e., not effectively just for TDX if possible: Currently the TDP MMU hooks are called depending whether the page table type is private (or mirrored whatever), but I think conceptually, we should decide whether to call TDP MMU hooks based on whether faulting GPA is private, _AND_ when the hook is available. https://lore.kernel.org/lkml/5e8119c0-31f5-4aa9-a496-4ae10bd745a3@intel.com/ If invoking SNP RMP commands is feasible in TDP MMU hooks, then I think there's value of letting SNP code to use them too. And we can simply split one patch out to only add the TDP MMU hooks for SNP to land first.
diff --git a/arch/x86/kvm/Kconfig b/arch/x86/kvm/Kconfig index 5e72faca4e8f..10768f13b240 100644 --- a/arch/x86/kvm/Kconfig +++ b/arch/x86/kvm/Kconfig @@ -137,6 +137,7 @@ config KVM_AMD_SEV depends on CRYPTO_DEV_SP_PSP && !(KVM_AMD=y && CRYPTO_DEV_CCP_DD=m) select ARCH_HAS_CC_PLATFORM select KVM_GENERIC_PRIVATE_MEM + select HAVE_KVM_GMEM_PREPARE help Provides support for launching Encrypted VMs (SEV) and Encrypted VMs with Encrypted State (SEV-ES) on AMD processors. diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c index 69ec8f577763..0439ec12fa90 100644 --- a/arch/x86/kvm/svm/sev.c +++ b/arch/x86/kvm/svm/sev.c @@ -4557,3 +4557,101 @@ void sev_handle_rmp_fault(struct kvm_vcpu *vcpu, gpa_t gpa, u64 error_code) out_no_trace: put_page(pfn_to_page(pfn)); } + +static bool is_pfn_range_shared(kvm_pfn_t start, kvm_pfn_t end) +{ + kvm_pfn_t pfn = start; + + while (pfn < end) { + int ret, rmp_level; + bool assigned; + + ret = snp_lookup_rmpentry(pfn, &assigned, &rmp_level); + if (ret) { + pr_warn_ratelimited("SEV: Failed to retrieve RMP entry: PFN 0x%llx GFN start 0x%llx GFN end 0x%llx RMP level %d error %d\n", + pfn, start, end, rmp_level, ret); + return false; + } + + if (assigned) { + pr_debug("%s: overlap detected, PFN 0x%llx start 0x%llx end 0x%llx RMP level %d\n", + __func__, pfn, start, end, rmp_level); + return false; + } + + pfn++; + } + + return true; +} + +static u8 max_level_for_order(int order) +{ + if (order >= KVM_HPAGE_GFN_SHIFT(PG_LEVEL_2M)) + return PG_LEVEL_2M; + + return PG_LEVEL_4K; +} + +static bool is_large_rmp_possible(struct kvm *kvm, kvm_pfn_t pfn, int order) +{ + kvm_pfn_t pfn_aligned = ALIGN_DOWN(pfn, PTRS_PER_PMD); + + /* + * If this is a large folio, and the entire 2M range containing the + * PFN is currently shared, then the entire 2M-aligned range can be + * set to private via a single 2M RMP entry. + */ + if (max_level_for_order(order) > PG_LEVEL_4K && + is_pfn_range_shared(pfn_aligned, pfn_aligned + PTRS_PER_PMD)) + return true; + + return false; +} + +int sev_gmem_prepare(struct kvm *kvm, kvm_pfn_t pfn, gfn_t gfn, int max_order) +{ + struct kvm_sev_info *sev = &to_kvm_svm(kvm)->sev_info; + kvm_pfn_t pfn_aligned; + gfn_t gfn_aligned; + int level, rc; + bool assigned; + + if (!sev_snp_guest(kvm)) + return 0; + + rc = snp_lookup_rmpentry(pfn, &assigned, &level); + if (rc) { + pr_err_ratelimited("SEV: Failed to look up RMP entry: GFN %llx PFN %llx error %d\n", + gfn, pfn, rc); + return -ENOENT; + } + + if (assigned) { + pr_debug("%s: already assigned: gfn %llx pfn %llx max_order %d level %d\n", + __func__, gfn, pfn, max_order, level); + return 0; + } + + if (is_large_rmp_possible(kvm, pfn, max_order)) { + level = PG_LEVEL_2M; + pfn_aligned = ALIGN_DOWN(pfn, PTRS_PER_PMD); + gfn_aligned = ALIGN_DOWN(gfn, PTRS_PER_PMD); + } else { + level = PG_LEVEL_4K; + pfn_aligned = pfn; + gfn_aligned = gfn; + } + + rc = rmp_make_private(pfn_aligned, gfn_to_gpa(gfn_aligned), level, sev->asid, false); + if (rc) { + pr_err_ratelimited("SEV: Failed to update RMP entry: GFN %llx PFN %llx level %d error %d\n", + gfn, pfn, level, rc); + return -EINVAL; + } + + pr_debug("%s: updated: gfn %llx pfn %llx pfn_aligned %llx max_order %d level %d\n", + __func__, gfn, pfn, pfn_aligned, max_order, level); + + return 0; +} diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c index b70556608e8d..60783e9f2ae8 100644 --- a/arch/x86/kvm/svm/svm.c +++ b/arch/x86/kvm/svm/svm.c @@ -5085,6 +5085,8 @@ static struct kvm_x86_ops svm_x86_ops __initdata = { .vcpu_deliver_sipi_vector = svm_vcpu_deliver_sipi_vector, .vcpu_get_apicv_inhibit_reasons = avic_vcpu_get_apicv_inhibit_reasons, .alloc_apic_backing_page = svm_alloc_apic_backing_page, + + .gmem_prepare = sev_gmem_prepare, }; /* diff --git a/arch/x86/kvm/svm/svm.h b/arch/x86/kvm/svm/svm.h index 858e74a26fab..ff1aca7e10e9 100644 --- a/arch/x86/kvm/svm/svm.h +++ b/arch/x86/kvm/svm/svm.h @@ -736,6 +736,7 @@ extern unsigned int max_sev_asid; void sev_handle_rmp_fault(struct kvm_vcpu *vcpu, gpa_t gpa, u64 error_code); void sev_vcpu_unblocking(struct kvm_vcpu *vcpu); void sev_snp_init_protected_guest_state(struct kvm_vcpu *vcpu); +int sev_gmem_prepare(struct kvm *kvm, kvm_pfn_t pfn, gfn_t gfn, int max_order); #else static inline struct page *snp_safe_alloc_page(struct kvm_vcpu *vcpu) { return alloc_page(GFP_KERNEL_ACCOUNT | __GFP_ZERO); @@ -752,6 +753,10 @@ static inline int sev_dev_get_attr(u32 group, u64 attr, u64 *val) { return -ENXI static inline void sev_handle_rmp_fault(struct kvm_vcpu *vcpu, gpa_t gpa, u64 error_code) {} static inline void sev_vcpu_unblocking(struct kvm_vcpu *vcpu) {} static inline void sev_snp_init_protected_guest_state(struct kvm_vcpu *vcpu) {} +static inline int sev_gmem_prepare(struct kvm *kvm, kvm_pfn_t pfn, gfn_t gfn, int max_order) +{ + return 0; +} #endif diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index b20f6c1b8214..0fb76ef9b7e9 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -13610,6 +13610,11 @@ bool kvm_arch_no_poll(struct kvm_vcpu *vcpu) EXPORT_SYMBOL_GPL(kvm_arch_no_poll); #ifdef CONFIG_HAVE_KVM_GMEM_PREPARE +bool kvm_arch_gmem_prepare_needed(struct kvm *kvm) +{ + return kvm->arch.vm_type == KVM_X86_SNP_VM; +} + int kvm_arch_gmem_prepare(struct kvm *kvm, gfn_t gfn, kvm_pfn_t pfn, int max_order) { return static_call(kvm_x86_gmem_prepare)(kvm, pfn, gfn, max_order); diff --git a/virt/kvm/guest_memfd.c b/virt/kvm/guest_memfd.c index a44f983eb673..7d3932e5a689 100644 --- a/virt/kvm/guest_memfd.c +++ b/virt/kvm/guest_memfd.c @@ -46,8 +46,8 @@ static int kvm_gmem_prepare_folio(struct inode *inode, pgoff_t index, struct fol gfn = slot->base_gfn + index - slot->gmem.pgoff; rc = kvm_arch_gmem_prepare(kvm, gfn, pfn, compound_order(compound_head(page))); if (rc) { - pr_warn_ratelimited("gmem: Failed to prepare folio for index %lx, error %d.\n", - index, rc); + pr_warn_ratelimited("gmem: Failed to prepare folio for index %lx GFN %llx PFN %llx error %d.\n", + index, gfn, pfn, rc); return rc; } }