Re: [PATCH v19 038/130] KVM: TDX: create/destroy VM structure

Isaku Yamahata
2024-03-21T14:17:11Z

On Wed, Mar 20, 2024 at 01:12:01PM +0800,
Chao Gao <chao.gao@intel.com> wrote:

> > config KVM_SW_PROTECTED_VM
> > bool "Enable support for KVM software-protected VMs"
> >- depends on EXPERT
> > depends on KVM && X86_64
> > select KVM_GENERIC_PRIVATE_MEM
> > help
> >@@ -89,6 +88,8 @@ config KVM_SW_PROTECTED_VM
> > config KVM_INTEL
> > tristate "KVM for Intel (and compatible) processors support"
> > depends on KVM && IA32_FEAT_CTL
> >+ select KVM_SW_PROTECTED_VM if INTEL_TDX_HOST
>
> why does INTEL_TDX_HOST select KVM_SW_PROTECTED_VM?

I wanted KVM_GENERIC_PRIVATE_MEM. Ah, we should do

select KKVM_GENERIC_PRIVATE_MEM if INTEL_TDX_HOST

> >+ select KVM_GENERIC_MEMORY_ATTRIBUTES if INTEL_TDX_HOST
> > help
> > .vcpu_precreate = vmx_vcpu_precreate,
> > .vcpu_create = vmx_vcpu_create,
>
> >--- a/arch/x86/kvm/vmx/tdx.c
> >+++ b/arch/x86/kvm/vmx/tdx.c
> >@@ -5,10 +5,11 @@
> >
> > #include "capabilities.h"
> > #include "x86_ops.h"
> >-#include "x86.h"
> > #include "mmu.h"
> > #include "tdx_arch.h"
> > #include "tdx.h"
> >+#include "tdx_ops.h"
> >+#include "x86.h"
>
> any reason to reorder x86.h?

No, I think it's accidental during rebase.
Will fix.

> >+static void tdx_do_tdh_phymem_cache_wb(void *unused)
> >+{
> >+ u64 err = 0;
> >+
> >+ do {
> >+ err = tdh_phymem_cache_wb(!!err);
> >+ } while (err == TDX_INTERRUPTED_RESUMABLE);
> >+
> >+ /* Other thread may have done for us. */
> >+ if (err == TDX_NO_HKID_READY_TO_WBCACHE)
> >+ err = TDX_SUCCESS;
> >+ if (WARN_ON_ONCE(err))
> >+ pr_tdx_error(TDH_PHYMEM_CACHE_WB, err, NULL);
> >+}
> >+
> >+void tdx_mmu_release_hkid(struct kvm *kvm)
> >+{
> >+ bool packages_allocated, targets_allocated;
> >+ struct kvm_tdx *kvm_tdx = to_kvm_tdx(kvm);
> >+ cpumask_var_t packages, targets;
> >+ u64 err;
> >+ int i;
> >+
> >+ if (!is_hkid_assigned(kvm_tdx))
> >+ return;
> >+
> >+ if (!is_td_created(kvm_tdx)) {
> >+ tdx_hkid_free(kvm_tdx);
> >+ return;
> >+ }
> >+
> >+ packages_allocated = zalloc_cpumask_var(&packages, GFP_KERNEL);
> >+ targets_allocated = zalloc_cpumask_var(&targets, GFP_KERNEL);
> >+ cpus_read_lock();
> >+
> >+ /*
> >+ * We can destroy multiple guest TDs simultaneously. Prevent
> >+ * tdh_phymem_cache_wb from returning TDX_BUSY by serialization.
> >+ */
> >+ mutex_lock(&tdx_lock);
> >+
> >+ /*
> >+ * Go through multiple TDX HKID state transitions with three SEAMCALLs
> >+ * to make TDH.PHYMEM.PAGE.RECLAIM() usable. Make the transition atomic
> >+ * to other functions to operate private pages and Secure-EPT pages.
> >+ *
> >+ * Avoid race for kvm_gmem_release() to call kvm_mmu_unmap_gfn_range().
> >+ * This function is called via mmu notifier, mmu_release().
> >+ * kvm_gmem_release() is called via fput() on process exit.
> >+ */
> >+ write_lock(&kvm->mmu_lock);
> >+
> >+ for_each_online_cpu(i) {
> >+ if (packages_allocated &&
> >+ cpumask_test_and_set_cpu(topology_physical_package_id(i),
> >+ packages))
> >+ continue;
> >+ if (targets_allocated)
> >+ cpumask_set_cpu(i, targets);
> >+ }
> >+ if (targets_allocated)
> >+ on_each_cpu_mask(targets, tdx_do_tdh_phymem_cache_wb, NULL, true);
> >+ else
> >+ on_each_cpu(tdx_do_tdh_phymem_cache_wb, NULL, true);
>
> This tries flush cache on all CPUs when we run out of memory. I am not sure if
> it is the best solution. A simple solution is just use two global bitmaps.
>
> And current logic isn't optimal. e.g., if packages_allocated is true while
> targets_allocated is false, then we will fill in the packages bitmap but don't
> use it at all.
>
> That said, I prefer to optimize the rare case in a separate patch. We can just use
> two global bitmaps or let the flush fail here just as you are doing below on
> seamcall failure.

Makes sense. We can allocate cpumasks on hardware_setup/unsetup() and update them
on hardware_enable/disable().

...

> >+static int __tdx_td_init(struct kvm *kvm)
> >+{
> >+ struct kvm_tdx *kvm_tdx = to_kvm_tdx(kvm);
> >+ cpumask_var_t packages;
> >+ unsigned long *tdcs_pa = NULL;
> >+ unsigned long tdr_pa = 0;
> >+ unsigned long va;
> >+ int ret, i;
> >+ u64 err;
> >+
> >+ ret = tdx_guest_keyid_alloc();
> >+ if (ret < 0)
> >+ return ret;
> >+ kvm_tdx->hkid = ret;
> >+
> >+ va = __get_free_page(GFP_KERNEL_ACCOUNT);
> >+ if (!va)
> >+ goto free_hkid;
> >+ tdr_pa = __pa(va);
> >+
> >+ tdcs_pa = kcalloc(tdx_info->nr_tdcs_pages, sizeof(*kvm_tdx->tdcs_pa),
> >+ GFP_KERNEL_ACCOUNT | __GFP_ZERO);
> >+ if (!tdcs_pa)
> >+ goto free_tdr;
> >+ for (i = 0; i < tdx_info->nr_tdcs_pages; i++) {
> >+ va = __get_free_page(GFP_KERNEL_ACCOUNT);
> >+ if (!va)
> >+ goto free_tdcs;
> >+ tdcs_pa[i] = __pa(va);
> >+ }
> >+
> >+ if (!zalloc_cpumask_var(&packages, GFP_KERNEL)) {
> >+ ret = -ENOMEM;
> >+ goto free_tdcs;
> >+ }
> >+ cpus_read_lock();
> >+ /*
> >+ * Need at least one CPU of the package to be online in order to
> >+ * program all packages for host key id. Check it.
> >+ */
> >+ for_each_present_cpu(i)
> >+ cpumask_set_cpu(topology_physical_package_id(i), packages);
> >+ for_each_online_cpu(i)
> >+ cpumask_clear_cpu(topology_physical_package_id(i), packages);
> >+ if (!cpumask_empty(packages)) {
> >+ ret = -EIO;
> >+ /*
> >+ * Because it's hard for human operator to figure out the
> >+ * reason, warn it.
> >+ */
> >+#define MSG_ALLPKG "All packages need to have online CPU to create TD. Online CPU and retry.\n"
> >+ pr_warn_ratelimited(MSG_ALLPKG);
> >+ goto free_packages;
> >+ }
> >+
> >+ /*
> >+ * Acquire global lock to avoid TDX_OPERAND_BUSY:
> >+ * TDH.MNG.CREATE and other APIs try to lock the global Key Owner
> >+ * Table (KOT) to track the assigned TDX private HKID. It doesn't spin
> >+ * to acquire the lock, returns TDX_OPERAND_BUSY instead, and let the
> >+ * caller to handle the contention. This is because of time limitation
> >+ * usable inside the TDX module and OS/VMM knows better about process
> >+ * scheduling.
> >+ *
> >+ * APIs to acquire the lock of KOT:
> >+ * TDH.MNG.CREATE, TDH.MNG.KEY.FREEID, TDH.MNG.VPFLUSHDONE, and
> >+ * TDH.PHYMEM.CACHE.WB.
> >+ */
> >+ mutex_lock(&tdx_lock);
> >+ err = tdh_mng_create(tdr_pa, kvm_tdx->hkid);
> >+ mutex_unlock(&tdx_lock);
> >+ if (err == TDX_RND_NO_ENTROPY) {
> >+ ret = -EAGAIN;
> >+ goto free_packages;
> >+ }
> >+ if (WARN_ON_ONCE(err)) {
> >+ pr_tdx_error(TDH_MNG_CREATE, err, NULL);
> >+ ret = -EIO;
> >+ goto free_packages;
> >+ }
> >+ kvm_tdx->tdr_pa = tdr_pa;
> >+
> >+ for_each_online_cpu(i) {
> >+ int pkg = topology_physical_package_id(i);
> >+
> >+ if (cpumask_test_and_set_cpu(pkg, packages))
> >+ continue;
> >+
> >+ /*
> >+ * Program the memory controller in the package with an
> >+ * encryption key associated to a TDX private host key id
> >+ * assigned to this TDR. Concurrent operations on same memory
> >+ * controller results in TDX_OPERAND_BUSY. Avoid this race by
> >+ * mutex.
> >+ */
> >+ mutex_lock(&tdx_mng_key_config_lock[pkg]);
>
> the lock is superfluous to me. with cpu lock held, even if multiple CPUs try to
> create TDs, the same set of CPUs (the first online CPU of each package) will be
> selected to configure the key because of the cpumask_test_and_set_cpu() above.
> it means, we never have two CPUs in the same socket trying to program the key,
> i.e., no concurrent calls.

Makes sense. Will drop the lock.

> >+ ret = smp_call_on_cpu(i, tdx_do_tdh_mng_key_config,
> >+ &kvm_tdx->tdr_pa, true);
> >+ mutex_unlock(&tdx_mng_key_config_lock[pkg]);
> >+ if (ret)
> >+ break;
> >+ }
> >+ cpus_read_unlock();
> >+ free_cpumask_var(packages);
> >+ if (ret) {
> >+ i = 0;
> >+ goto teardown;
> >+ }
> >+
> >+ kvm_tdx->tdcs_pa = tdcs_pa;
> >+ for (i = 0; i < tdx_info->nr_tdcs_pages; i++) {
> >+ err = tdh_mng_addcx(kvm_tdx->tdr_pa, tdcs_pa[i]);
> >+ if (err == TDX_RND_NO_ENTROPY) {
> >+ /* Here it's hard to allow userspace to retry. */
> >+ ret = -EBUSY;
> >+ goto teardown;
> >+ }
> >+ if (WARN_ON_ONCE(err)) {
> >+ pr_tdx_error(TDH_MNG_ADDCX, err, NULL);
> >+ ret = -EIO;
> >+ goto teardown;
> >+ }
> >+ }
> >+
> >+ /*
> >+ * Note, TDH_MNG_INIT cannot be invoked here. TDH_MNG_INIT requires a dedicated
> >+ * ioctl() to define the configure CPUID values for the TD.
> >+ */
> >+ return 0;
> >+
> >+ /*
> >+ * The sequence for freeing resources from a partially initialized TD
> >+ * varies based on where in the initialization flow failure occurred.
> >+ * Simply use the full teardown and destroy, which naturally play nice
> >+ * with partial initialization.
> >+ */
> >+teardown:
> >+ for (; i < tdx_info->nr_tdcs_pages; i++) {
> >+ if (tdcs_pa[i]) {
> >+ free_page((unsigned long)__va(tdcs_pa[i]));
> >+ tdcs_pa[i] = 0;
> >+ }
> >+ }
> >+ if (!kvm_tdx->tdcs_pa)
> >+ kfree(tdcs_pa);
> >+ tdx_mmu_release_hkid(kvm);
> >+ tdx_vm_free(kvm);
> >+ return ret;
> >+
> >+free_packages:
> >+ cpus_read_unlock();
> >+ free_cpumask_var(packages);
> >+free_tdcs:
> >+ for (i = 0; i < tdx_info->nr_tdcs_pages; i++) {
> >+ if (tdcs_pa[i])
> >+ free_page((unsigned long)__va(tdcs_pa[i]));
> >+ }
> >+ kfree(tdcs_pa);
> >+ kvm_tdx->tdcs_pa = NULL;
> >+
> >+free_tdr:
> >+ if (tdr_pa)
> >+ free_page((unsigned long)__va(tdr_pa));
> >+ kvm_tdx->tdr_pa = 0;
> >+free_hkid:
> >+ if (is_hkid_assigned(kvm_tdx))
>
> IIUC, this is always true because you just return if keyid
> allocation fails.

You're right. Will fix
--
Isaku Yamahata <isaku.yamahata@intel.com>