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Message-ID: <Ztfn5gh5888PmEIe@yzhao56-desk.sh.intel.com>
Date: Wed, 4 Sep 2024 12:53:58 +0800
From: Yan Zhao <yan.y.zhao@...el.com>
To: Rick Edgecombe <rick.p.edgecombe@...el.com>
CC: <seanjc@...gle.com>, <pbonzini@...hat.com>, <kvm@...r.kernel.org>,
<kai.huang@...el.com>, <dmatlack@...gle.com>, <isaku.yamahata@...il.com>,
<nik.borisov@...e.com>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 19/21] KVM: TDX: Add an ioctl to create initial guest
memory
On Tue, Sep 03, 2024 at 08:07:49PM -0700, Rick Edgecombe wrote:
> From: Isaku Yamahata <isaku.yamahata@...el.com>
>
> Add a new ioctl for the user space VMM to initialize guest memory with the
> specified memory contents.
>
> Because TDX protects the guest's memory, the creation of the initial guest
> memory requires a dedicated TDX module API, TDH.MEM.PAGE.ADD(), instead of
> directly copying the memory contents into the guest's memory in the case of
> the default VM type.
>
> Define a new subcommand, KVM_TDX_INIT_MEM_REGION, of vCPU-scoped
> KVM_MEMORY_ENCRYPT_OP. Check if the GFN is already pre-allocated, assign
> the guest page in Secure-EPT, copy the initial memory contents into the
> guest memory, and encrypt the guest memory. Optionally, extend the memory
> measurement of the TDX guest.
>
> Discussion history:
> - Originally, KVM_TDX_INIT_MEM_REGION used the callback of the TDP MMU of
> the KVM page fault handler. It issues TDX SEAMCALL deep in the call
> stack, and the ioctl passes down the necessary parameters. [2] rejected
> it. [3] suggests that the call to the TDX module should be invoked in a
> shallow call stack.
>
> - Instead, introduce guest memory pre-population [1] that doesn't update
> vendor-specific part (Secure-EPT in TDX case) and the vendor-specific
> code (KVM_TDX_INIT_MEM_REGION) updates only vendor-specific parts without
> modifying the KVM TDP MMU suggested at [4]
>
> Crazy idea. For TDX S-EPT, what if KVM_MAP_MEMORY does all of the
> SEPT.ADD stuff, which doesn't affect the measurement, and even fills in
> KVM's copy of the leaf EPTE, but tdx_sept_set_private_spte() doesn't do
> anything if the TD isn't finalized?
>
> Then KVM provides a dedicated TDX ioctl(), i.e. what is/was
> KVM_TDX_INIT_MEM_REGION, to do PAGE.ADD. KVM_TDX_INIT_MEM_REGION
> wouldn't need to map anything, it would simply need to verify that the
> pfn from guest_memfd() is the same as what's in the TDP MMU.
>
> - Use the common guest_memfd population function, kvm_gmem_populate()
> instead of a custom function. It should check whether the PFN
> from TDP MMU is the same as the one from guest_memfd. [1]
>
> - Instead of forcing userspace to do two passes, pre-map the guest
> initial memory in tdx_gmem_post_populate. [5]
>
> Link: https://lore.kernel.org/kvm/20240419085927.3648704-1-pbonzini@redhat.com/ [1]
> Link: https://lore.kernel.org/kvm/Zbrj5WKVgMsUFDtb@google.com/ [2]
> Link: https://lore.kernel.org/kvm/Zh8DHbb8FzoVErgX@google.com/ [3]
> Link: https://lore.kernel.org/kvm/Ze-TJh0BBOWm9spT@google.com/ [4]
> Link: https://lore.kernel.org/kvm/CABgObfa=a3cKcKJHQRrCs-3Ty8ppSRou=dhi6Q+KdZnom0Zegw@mail.gmail.com/ [5]
> Suggested-by: Sean Christopherson <seanjc@...gle.com>
> Signed-off-by: Isaku Yamahata <isaku.yamahata@...el.com>
> Co-developed-by: Yan Zhao <yan.y.zhao@...el.com>
> Signed-off-by: Yan Zhao <yan.y.zhao@...el.com>
> Signed-off-by: Rick Edgecombe <rick.p.edgecombe@...el.com>
> ---
> TDX MMU part 2 v1:
> - Update the code according to latest gmem update.
> https://lore.kernel.org/kvm/CABgObfa=a3cKcKJHQRrCs-3Ty8ppSRou=dhi6Q+KdZnom0Zegw@mail.gmail.com/
> - Fixup a aligment bug reported by Binbin.
> - Rename KVM_MEMORY_MAPPING => KVM_MAP_MEMORY (Sean)
> - Drop issueing TDH.MEM.PAGE.ADD() on KVM_MAP_MEMORY(), defer it to
> KVM_TDX_INIT_MEM_REGION. (Sean)
> - Added nr_premapped to track the number of premapped pages
> - Drop tdx_post_mmu_map_page().
> - Drop kvm_slot_can_be_private() check (Paolo)
> - Use kvm_tdp_mmu_gpa_is_mapped() (Paolo)
>
> v19:
> - Switched to use KVM_MEMORY_MAPPING
> - Dropped measurement extension
> - updated commit message. private_page_add() => set_private_spte()
> ---
> arch/x86/include/uapi/asm/kvm.h | 9 ++
> arch/x86/kvm/vmx/tdx.c | 150 ++++++++++++++++++++++++++++++++
> virt/kvm/kvm_main.c | 1 +
> 3 files changed, 160 insertions(+)
>
> diff --git a/arch/x86/include/uapi/asm/kvm.h b/arch/x86/include/uapi/asm/kvm.h
> index 39636be5c891..789d1d821b4f 100644
> --- a/arch/x86/include/uapi/asm/kvm.h
> +++ b/arch/x86/include/uapi/asm/kvm.h
> @@ -931,6 +931,7 @@ enum kvm_tdx_cmd_id {
> KVM_TDX_CAPABILITIES = 0,
> KVM_TDX_INIT_VM,
> KVM_TDX_INIT_VCPU,
> + KVM_TDX_INIT_MEM_REGION,
> KVM_TDX_GET_CPUID,
>
> KVM_TDX_CMD_NR_MAX,
> @@ -996,4 +997,12 @@ struct kvm_tdx_init_vm {
> struct kvm_cpuid2 cpuid;
> };
>
> +#define KVM_TDX_MEASURE_MEMORY_REGION _BITULL(0)
> +
> +struct kvm_tdx_init_mem_region {
> + __u64 source_addr;
> + __u64 gpa;
> + __u64 nr_pages;
> +};
> +
> #endif /* _ASM_X86_KVM_H */
> diff --git a/arch/x86/kvm/vmx/tdx.c b/arch/x86/kvm/vmx/tdx.c
> index 50ce24905062..796d1a495a66 100644
> --- a/arch/x86/kvm/vmx/tdx.c
> +++ b/arch/x86/kvm/vmx/tdx.c
> @@ -8,6 +8,7 @@
> #include "tdx_ops.h"
> #include "vmx.h"
> #include "mmu/spte.h"
> +#include "common.h"
>
> #undef pr_fmt
> #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
> @@ -1586,6 +1587,152 @@ static int tdx_vcpu_init(struct kvm_vcpu *vcpu, struct kvm_tdx_cmd *cmd)
> return 0;
> }
>
> +struct tdx_gmem_post_populate_arg {
> + struct kvm_vcpu *vcpu;
> + __u32 flags;
> +};
> +
> +static int tdx_gmem_post_populate(struct kvm *kvm, gfn_t gfn, kvm_pfn_t pfn,
> + void __user *src, int order, void *_arg)
> +{
> + u64 error_code = PFERR_GUEST_FINAL_MASK | PFERR_PRIVATE_ACCESS;
> + struct kvm_tdx *kvm_tdx = to_kvm_tdx(kvm);
> + struct tdx_gmem_post_populate_arg *arg = _arg;
> + struct kvm_vcpu *vcpu = arg->vcpu;
> + gpa_t gpa = gfn_to_gpa(gfn);
> + u8 level = PG_LEVEL_4K;
> + struct page *page;
> + int ret, i;
> + u64 err, entry, level_state;
> +
> + /*
> + * Get the source page if it has been faulted in. Return failure if the
> + * source page has been swapped out or unmapped in primary memory.
> + */
> + ret = get_user_pages_fast((unsigned long)src, 1, 0, &page);
> + if (ret < 0)
> + return ret;
> + if (ret != 1)
> + return -ENOMEM;
> +
> + if (!kvm_mem_is_private(kvm, gfn)) {
> + ret = -EFAULT;
> + goto out_put_page;
> + }
> +
> + ret = kvm_tdp_map_page(vcpu, gpa, error_code, &level);
> + if (ret < 0)
> + goto out_put_page;
> +
> + read_lock(&kvm->mmu_lock);
Although mirrored root can't be zapped with shared lock currently, is it
better to hold write_lock() here?
It should bring no extra overhead in a normal condition when the
tdx_gmem_post_populate() is called.
> +
> + if (!kvm_tdp_mmu_gpa_is_mapped(vcpu, gpa)) {
> + ret = -ENOENT;
> + goto out;
> + }
> +
> + ret = 0;
> + do {
> + err = tdh_mem_page_add(kvm_tdx, gpa, pfn_to_hpa(pfn),
> + pfn_to_hpa(page_to_pfn(page)),
> + &entry, &level_state);
> + } while (err == TDX_ERROR_SEPT_BUSY);
> + if (err) {
> + ret = -EIO;
> + goto out;
> + }
> +
> + WARN_ON_ONCE(!atomic64_read(&kvm_tdx->nr_premapped));
> + atomic64_dec(&kvm_tdx->nr_premapped);
> +
> + if (arg->flags & KVM_TDX_MEASURE_MEMORY_REGION) {
> + for (i = 0; i < PAGE_SIZE; i += TDX_EXTENDMR_CHUNKSIZE) {
> + err = tdh_mr_extend(kvm_tdx, gpa + i, &entry,
> + &level_state);
> + if (err) {
> + ret = -EIO;
> + break;
> + }
> + }
> + }
> +
> +out:
> + read_unlock(&kvm->mmu_lock);
> +out_put_page:
> + put_page(page);
> + return ret;
> +}
> +
> +static int tdx_vcpu_init_mem_region(struct kvm_vcpu *vcpu, struct kvm_tdx_cmd *cmd)
> +{
> + struct kvm *kvm = vcpu->kvm;
> + struct kvm_tdx *kvm_tdx = to_kvm_tdx(kvm);
> + struct kvm_tdx_init_mem_region region;
> + struct tdx_gmem_post_populate_arg arg;
> + long gmem_ret;
> + int ret;
> +
> + if (!to_tdx(vcpu)->initialized)
> + return -EINVAL;
> +
> + /* Once TD is finalized, the initial guest memory is fixed. */
> + if (is_td_finalized(kvm_tdx))
> + return -EINVAL;
> +
> + if (cmd->flags & ~KVM_TDX_MEASURE_MEMORY_REGION)
> + return -EINVAL;
> +
> + if (copy_from_user(®ion, u64_to_user_ptr(cmd->data), sizeof(region)))
> + return -EFAULT;
> +
> + if (!PAGE_ALIGNED(region.source_addr) || !PAGE_ALIGNED(region.gpa) ||
> + !region.nr_pages ||
> + region.gpa + (region.nr_pages << PAGE_SHIFT) <= region.gpa ||
> + !kvm_is_private_gpa(kvm, region.gpa) ||
> + !kvm_is_private_gpa(kvm, region.gpa + (region.nr_pages << PAGE_SHIFT) - 1))
> + return -EINVAL;
> +
> + mutex_lock(&kvm->slots_lock);
> +
> + kvm_mmu_reload(vcpu);
> + ret = 0;
> + while (region.nr_pages) {
> + if (signal_pending(current)) {
> + ret = -EINTR;
> + break;
> + }
> +
> + arg = (struct tdx_gmem_post_populate_arg) {
> + .vcpu = vcpu,
> + .flags = cmd->flags,
> + };
> + gmem_ret = kvm_gmem_populate(kvm, gpa_to_gfn(region.gpa),
> + u64_to_user_ptr(region.source_addr),
> + 1, tdx_gmem_post_populate, &arg);
> + if (gmem_ret < 0) {
> + ret = gmem_ret;
> + break;
> + }
> +
> + if (gmem_ret != 1) {
> + ret = -EIO;
> + break;
> + }
> +
> + region.source_addr += PAGE_SIZE;
> + region.gpa += PAGE_SIZE;
> + region.nr_pages--;
> +
> + cond_resched();
> + }
> +
> + mutex_unlock(&kvm->slots_lock);
> +
> + if (copy_to_user(u64_to_user_ptr(cmd->data), ®ion, sizeof(region)))
> + ret = -EFAULT;
> + return ret;
> +}
> +
> int tdx_vcpu_ioctl(struct kvm_vcpu *vcpu, void __user *argp)
> {
> struct kvm_tdx *kvm_tdx = to_kvm_tdx(vcpu->kvm);
> @@ -1605,6 +1752,9 @@ int tdx_vcpu_ioctl(struct kvm_vcpu *vcpu, void __user *argp)
> case KVM_TDX_INIT_VCPU:
> ret = tdx_vcpu_init(vcpu, &cmd);
> break;
> + case KVM_TDX_INIT_MEM_REGION:
> + ret = tdx_vcpu_init_mem_region(vcpu, &cmd);
> + break;
> case KVM_TDX_GET_CPUID:
> ret = tdx_vcpu_get_cpuid(vcpu, &cmd);
> break;
> diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> index 73fc3334721d..0822db480719 100644
> --- a/virt/kvm/kvm_main.c
> +++ b/virt/kvm/kvm_main.c
> @@ -2639,6 +2639,7 @@ struct kvm_memory_slot *kvm_vcpu_gfn_to_memslot(struct kvm_vcpu *vcpu, gfn_t gfn
>
> return NULL;
> }
> +EXPORT_SYMBOL_GPL(kvm_vcpu_gfn_to_memslot);
>
> bool kvm_is_visible_gfn(struct kvm *kvm, gfn_t gfn)
> {
> --
> 2.34.1
>
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