Message-ID: <20240321141709.GK1994522@ls.amr.corp.intel.com>
Date: Thu, 21 Mar 2024 07:17:09 -0700
From: Isaku Yamahata <isaku.yamahata@...el.com>
To: Chao Gao <chao.gao@...el.com>
Cc: isaku.yamahata@...el.com, kvm@...r.kernel.org,
	linux-kernel@...r.kernel.org, isaku.yamahata@...il.com,
	Paolo Bonzini <pbonzini@...hat.com>, erdemaktas@...gle.com,
	Sean Christopherson <seanjc@...gle.com>,
	Sagi Shahar <sagis@...gle.com>, Kai Huang <kai.huang@...el.com>,
	chen.bo@...el.com, hang.yuan@...el.com, tina.zhang@...el.com,
	Sean Christopherson <sean.j.christopherson@...el.com>,
	isaku.yamahata@...ux.intel.com
Subject: Re: [PATCH v19 038/130] KVM: TDX: create/destroy VM structure

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

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