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

[Yuan Yao]

On Thu, Mar 21, 2024 at 07:17:09AM -0700, Isaku Yamahata wrote:
> On Wed, Mar 20, 2024 at 01:12:01PM +0800,
> Chao Gao <chao.gao@xxxxxxxxx> 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.

Not get the point, the variable "packages" on stack, and it's
possible that "i" is same for 2 threads which are trying to create td.
Anything I missed ?

>
>
> > >+		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@xxxxxxxxx>
>