On Mon, Apr 12, 2021 at 12:40:48PM +0200, Jan Beulich wrote: > The address of this page is used by the CPU only to recognize when to > access the virtual APIC page instead. No accesses would ever go to this > page. It only needs to be present in the (CPU) page tables so that > address translation will produce its address as result for respective > accesses. > > By making this page global, we also eliminate the need to refcount it, > or to assign it to any domain in the first place. > > Signed-off-by: Jan Beulich <jbeul...@suse.com> > Reviewed-by: Kevin Tian <kevin.t...@intel.com> > --- > v4: Set PGC_extra on the page. Make shadow mode work. > v3: Split p2m insertion change to a separate patch. > v2: Avoid insertion when !has_vlapic(). Split off change to > p2m_get_iommu_flags(). > --- > I did further consider not allocating any real page at all, but just > using the address of some unpopulated space (which would require > announcing this page as reserved to Dom0, so it wouldn't put any PCI > MMIO BARs there). But I thought this would be too controversial, because > of the possible risks associated with this.
Really seems more trouble than reward. Also there are systems with MMIO regions in holes on the memory map, like the issue I had with the Intel pinctrl stuff that had an MMIO region in a hole on the memory map [0], so I'm not sure Xen would be in a position to select a suitable unpopulated page anyway. [0] https://lore.kernel.org/xen-devel/yfx80wyt%2fkcha...@smile.fi.intel.com/ > --- a/xen/arch/x86/hvm/vmx/vmx.c > +++ b/xen/arch/x86/hvm/vmx/vmx.c > @@ -66,8 +66,7 @@ boolean_param("force-ept", opt_force_ept > static void vmx_ctxt_switch_from(struct vcpu *v); > static void vmx_ctxt_switch_to(struct vcpu *v); > > -static int vmx_alloc_vlapic_mapping(struct domain *d); > -static void vmx_free_vlapic_mapping(struct domain *d); > +static int alloc_vlapic_mapping(void); > static void vmx_install_vlapic_mapping(struct vcpu *v); > static void vmx_update_guest_cr(struct vcpu *v, unsigned int cr, > unsigned int flags); > @@ -78,6 +77,8 @@ static int vmx_msr_read_intercept(unsign > static int vmx_msr_write_intercept(unsigned int msr, uint64_t msr_content); > static void vmx_invlpg(struct vcpu *v, unsigned long linear); > > +static mfn_t __read_mostly apic_access_mfn; > + > /* Values for domain's ->arch.hvm_domain.pi_ops.flags. */ > #define PI_CSW_FROM (1u << 0) > #define PI_CSW_TO (1u << 1) > @@ -401,7 +402,6 @@ static int vmx_domain_initialise(struct > .to = vmx_ctxt_switch_to, > .tail = vmx_do_resume, > }; > - int rc; > > d->arch.ctxt_switch = &csw; > > @@ -411,28 +411,22 @@ static int vmx_domain_initialise(struct > */ > d->arch.hvm.vmx.exec_sp = is_hardware_domain(d) || opt_ept_exec_sp; > > - if ( !has_vlapic(d) ) > - return 0; > - > - if ( (rc = vmx_alloc_vlapic_mapping(d)) != 0 ) > - return rc; > - > return 0; > } > > -static void vmx_domain_relinquish_resources(struct domain *d) > +static void domain_creation_finished(struct domain *d) > { > - if ( !has_vlapic(d) ) > + gfn_t gfn = gaddr_to_gfn(APIC_DEFAULT_PHYS_BASE); Worth making it const static? > + uint8_t ipat; > + > + if ( !has_vlapic(d) || mfn_eq(apic_access_mfn, _mfn(0)) ) It would be better to use INVALID_MFN here, and init apic_access_mfn to that value. > return; > > - vmx_free_vlapic_mapping(d); > -} > + ASSERT(epte_get_entry_emt(d, gfn_x(gfn), apic_access_mfn, 0, &ipat, > + true) == MTRR_TYPE_WRBACK); > + ASSERT(ipat); > > -static void domain_creation_finished(struct domain *d) > -{ > - if ( has_vlapic(d) && !mfn_eq(d->arch.hvm.vmx.apic_access_mfn, _mfn(0)) > && > - set_mmio_p2m_entry(d, gaddr_to_gfn(APIC_DEFAULT_PHYS_BASE), > - d->arch.hvm.vmx.apic_access_mfn, PAGE_ORDER_4K) ) > + if ( set_mmio_p2m_entry(d, gfn, apic_access_mfn, PAGE_ORDER_4K) ) > domain_crash(d); > } > > @@ -2415,7 +2409,6 @@ static struct hvm_function_table __initd > .cpu_up_prepare = vmx_cpu_up_prepare, > .cpu_dead = vmx_cpu_dead, > .domain_initialise = vmx_domain_initialise, > - .domain_relinquish_resources = vmx_domain_relinquish_resources, > .domain_creation_finished = domain_creation_finished, > .vcpu_initialise = vmx_vcpu_initialise, > .vcpu_destroy = vmx_vcpu_destroy, > @@ -2662,7 +2655,7 @@ const struct hvm_function_table * __init > { > set_in_cr4(X86_CR4_VMXE); > > - if ( vmx_vmcs_init() ) > + if ( vmx_vmcs_init() || alloc_vlapic_mapping() ) > { > printk("VMX: failed to initialise.\n"); > return NULL; > @@ -3224,7 +3217,7 @@ gp_fault: > return X86EMUL_EXCEPTION; > } > > -static int vmx_alloc_vlapic_mapping(struct domain *d) > +static int __init alloc_vlapic_mapping(void) > { > struct page_info *pg; > mfn_t mfn; > @@ -3232,52 +3225,31 @@ static int vmx_alloc_vlapic_mapping(stru > if ( !cpu_has_vmx_virtualize_apic_accesses ) > return 0; > > - pg = alloc_domheap_page(d, MEMF_no_refcount); > + pg = alloc_domheap_page(NULL, 0); > if ( !pg ) > return -ENOMEM; > > - if ( !get_page_and_type(pg, d, PGT_writable_page) ) > - { > - /* > - * The domain can't possibly know about this page yet, so failure > - * here is a clear indication of something fishy going on. > - */ > - domain_crash(d); > - return -ENODATA; > - } > + /* Arrange for epte_get_entry_emt() to recognize this page as "special". > */ > + pg->count_info |= PGC_extra; > > mfn = page_to_mfn(pg); > clear_domain_page(mfn); > - d->arch.hvm.vmx.apic_access_mfn = mfn; > + apic_access_mfn = mfn; > > return 0; > } > > -static void vmx_free_vlapic_mapping(struct domain *d) > -{ > - mfn_t mfn = d->arch.hvm.vmx.apic_access_mfn; > - > - d->arch.hvm.vmx.apic_access_mfn = _mfn(0); > - if ( !mfn_eq(mfn, _mfn(0)) ) > - { > - struct page_info *pg = mfn_to_page(mfn); > - > - put_page_alloc_ref(pg); > - put_page_and_type(pg); > - } > -} > - > static void vmx_install_vlapic_mapping(struct vcpu *v) > { > paddr_t virt_page_ma, apic_page_ma; > > - if ( mfn_eq(v->domain->arch.hvm.vmx.apic_access_mfn, _mfn(0)) ) > + if ( !has_vlapic(v->domain) || mfn_eq(apic_access_mfn, _mfn(0)) ) > return; > > ASSERT(cpu_has_vmx_virtualize_apic_accesses); > > virt_page_ma = page_to_maddr(vcpu_vlapic(v)->regs_page); > - apic_page_ma = mfn_to_maddr(v->domain->arch.hvm.vmx.apic_access_mfn); > + apic_page_ma = mfn_to_maddr(apic_access_mfn); > > vmx_vmcs_enter(v); > __vmwrite(VIRTUAL_APIC_PAGE_ADDR, virt_page_ma); > --- a/xen/arch/x86/mm/shadow/set.c > +++ b/xen/arch/x86/mm/shadow/set.c > @@ -94,6 +94,22 @@ shadow_get_page_from_l1e(shadow_l1e_t sl > ASSERT(!sh_l1e_is_magic(sl1e)); > ASSERT(shadow_mode_refcounts(d)); > > + /* > + * VMX'es APIC access MFN is just a surrogate page. It doesn't actually > + * get accessed, and hence there's no need to refcount it (and > refcounting > + * would fail, due to the page having no owner). > + */ > + if ( mfn_valid(mfn = shadow_l1e_get_mfn(sl1e)) ) I find this assignment inside the parameter list quite ugly, I would rather split it on it's own line. > + { > + const struct page_info *pg = mfn_to_page(mfn); > + > + if ( !page_get_owner(pg) && (pg->count_info & PGC_extra) ) > + { > + ASSERT(type == p2m_mmio_direct); > + return 0; Are there any other pages that could pass this check? I don't think so, but wanted to assert. Thanks, Roger.
