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[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [PATCH v2 04/18] x86/pv: introduce function to populate perdomain area and use it to map Xen GDT
On Wed Jan 8, 2025 at 2:26 PM GMT, Roger Pau Monne wrote:
> The current code to update the Xen part of the GDT when running a PV guest
> relies on caching the direct map address of all the L1 tables used to map the
> GDT and LDT, so that entries can be modified.
>
> Introduce a new function that populates the per-domain region, either using
> the
> recursive linear mappings when the target vCPU is the current one, or by
> directly modifying the L1 table of the per-domain region.
>
> Using such function to populate per-domain addresses drops the need to keep a
> reference to per-domain L1 tables previously used to change the per-domain
> mappings.
>
> Signed-off-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
> ---
> xen/arch/x86/domain.c | 11 +++-
> xen/arch/x86/include/asm/desc.h | 6 +-
> xen/arch/x86/include/asm/mm.h | 2 +
> xen/arch/x86/include/asm/processor.h | 5 ++
> xen/arch/x86/mm.c | 88 ++++++++++++++++++++++++++++
> xen/arch/x86/smpboot.c | 6 +-
> xen/arch/x86/traps.c | 10 ++--
> 7 files changed, 113 insertions(+), 15 deletions(-)
>
> diff --git a/xen/arch/x86/domain.c b/xen/arch/x86/domain.c
> index 1f680bf176ee..0bd0ef7e40f4 100644
> --- a/xen/arch/x86/domain.c
> +++ b/xen/arch/x86/domain.c
> @@ -1953,9 +1953,14 @@ static always_inline bool need_full_gdt(const struct
> domain *d)
>
> static void update_xen_slot_in_full_gdt(const struct vcpu *v, unsigned int
> cpu)
> {
> - l1e_write(pv_gdt_ptes(v) + FIRST_RESERVED_GDT_PAGE,
> - !is_pv_32bit_vcpu(v) ? per_cpu(gdt_l1e, cpu)
> - : per_cpu(compat_gdt_l1e, cpu));
> + ASSERT(v != current);
For this assert, and others below. IIUC, curr_vcpu == current when we're
properly switched. When we're idling current == idle and curr_vcpu == prev_ctx.
Granted, calling this in the middle of a lazy idle loop would be weird, but
would it make sense for PT consistency to use curr_vcpu here...
> +
> + populate_perdomain_mapping(v,
> + GDT_VIRT_START(v) +
> + (FIRST_RESERVED_GDT_PAGE << PAGE_SHIFT),
> + !is_pv_32bit_vcpu(v) ? &per_cpu(gdt_mfn, cpu)
> + :
> &per_cpu(compat_gdt_mfn,
> + cpu), 1);
> }
>
> static void load_full_gdt(const struct vcpu *v, unsigned int cpu)
> diff --git a/xen/arch/x86/include/asm/desc.h b/xen/arch/x86/include/asm/desc.h
> index a1e0807d97ed..33981bfca588 100644
> --- a/xen/arch/x86/include/asm/desc.h
> +++ b/xen/arch/x86/include/asm/desc.h
> @@ -44,6 +44,8 @@
>
> #ifndef __ASSEMBLY__
>
> +#include <xen/mm-frame.h>
> +
> #define GUEST_KERNEL_RPL(d) (is_pv_32bit_domain(d) ? 1 : 3)
>
> /* Fix up the RPL of a guest segment selector. */
> @@ -212,10 +214,10 @@ struct __packed desc_ptr {
>
> extern seg_desc_t boot_gdt[];
> DECLARE_PER_CPU(seg_desc_t *, gdt);
> -DECLARE_PER_CPU(l1_pgentry_t, gdt_l1e);
> +DECLARE_PER_CPU(mfn_t, gdt_mfn);
> extern seg_desc_t boot_compat_gdt[];
> DECLARE_PER_CPU(seg_desc_t *, compat_gdt);
> -DECLARE_PER_CPU(l1_pgentry_t, compat_gdt_l1e);
> +DECLARE_PER_CPU(mfn_t, compat_gdt_mfn);
> DECLARE_PER_CPU(bool, full_gdt_loaded);
>
> static inline void lgdt(const struct desc_ptr *gdtr)
> diff --git a/xen/arch/x86/include/asm/mm.h b/xen/arch/x86/include/asm/mm.h
> index 6c7e66ee21ab..b50a51327b2b 100644
> --- a/xen/arch/x86/include/asm/mm.h
> +++ b/xen/arch/x86/include/asm/mm.h
> @@ -603,6 +603,8 @@ int compat_arch_memory_op(unsigned long cmd,
> XEN_GUEST_HANDLE_PARAM(void) arg);
> int create_perdomain_mapping(struct domain *d, unsigned long va,
> unsigned int nr, l1_pgentry_t **pl1tab,
> struct page_info **ppg);
> +void populate_perdomain_mapping(const struct vcpu *v, unsigned long va,
> + mfn_t *mfn, unsigned long nr);
> void destroy_perdomain_mapping(struct domain *d, unsigned long va,
> unsigned int nr);
> void free_perdomain_mappings(struct domain *d);
> diff --git a/xen/arch/x86/include/asm/processor.h
> b/xen/arch/x86/include/asm/processor.h
> index d247ef8dd226..82ee89f736c2 100644
> --- a/xen/arch/x86/include/asm/processor.h
> +++ b/xen/arch/x86/include/asm/processor.h
> @@ -243,6 +243,11 @@ static inline unsigned long cr3_pa(unsigned long cr3)
> return cr3 & X86_CR3_ADDR_MASK;
> }
>
> +static inline mfn_t cr3_mfn(unsigned long cr3)
> +{
> + return maddr_to_mfn(cr3_pa(cr3));
> +}
> +
> static inline unsigned int cr3_pcid(unsigned long cr3)
> {
> return IS_ENABLED(CONFIG_PV) ? cr3 & X86_CR3_PCID_MASK : 0;
> diff --git a/xen/arch/x86/mm.c b/xen/arch/x86/mm.c
> index 3d5dd22b6c36..0abea792486c 100644
> --- a/xen/arch/x86/mm.c
> +++ b/xen/arch/x86/mm.c
> @@ -6423,6 +6423,94 @@ int create_perdomain_mapping(struct domain *d,
> unsigned long va,
> return rc;
> }
>
> +void populate_perdomain_mapping(const struct vcpu *v, unsigned long va,
> + mfn_t *mfn, unsigned long nr)
> +{
> + l1_pgentry_t *l1tab = NULL, *pl1e;
> + const l3_pgentry_t *l3tab;
> + const l2_pgentry_t *l2tab;
> + struct domain *d = v->domain;
> +
> + ASSERT(va >= PERDOMAIN_VIRT_START &&
> + va < PERDOMAIN_VIRT_SLOT(PERDOMAIN_SLOTS));
> + ASSERT(!nr || !l3_table_offset(va ^ (va + nr * PAGE_SIZE - 1)));
> +
> + /* Use likely to force the optimization for the fast path. */
> + if ( likely(v == current) )
... and here? In particular I'd expect using curr_vcpu here means...
> + {
> + unsigned int i;
> +
> + /* Ensure page-tables are from current (if current != curr_vcpu). */
> + sync_local_execstate();
... this should not be needed.
> +
> + /* Fast path: get L1 entries using the recursive linear mappings. */
> + pl1e = &__linear_l1_table[l1_linear_offset(va)];
> +
> + for ( i = 0; i < nr; i++, pl1e++ )
> + {
> + if ( unlikely(perdomain_l1e_needs_freeing(*pl1e)) )
> + {
> + ASSERT_UNREACHABLE();
> + free_domheap_page(l1e_get_page(*pl1e));
> + }
> + l1e_write(pl1e, l1e_from_mfn(mfn[i], __PAGE_HYPERVISOR_RW));
> + }
> +
> + return;
> + }
> +
> + ASSERT(d->arch.perdomain_l3_pg);
> + l3tab = __map_domain_page(d->arch.perdomain_l3_pg);
> +
> + if ( unlikely(!(l3e_get_flags(l3tab[l3_table_offset(va)]) &
> + _PAGE_PRESENT)) )
> + {
> + unmap_domain_page(l3tab);
> + gprintk(XENLOG_ERR, "unable to map at VA %lx: L3e not present\n",
> va);
> + ASSERT_UNREACHABLE();
> + domain_crash(d);
> +
> + return;
> + }
> +
> + l2tab = map_l2t_from_l3e(l3tab[l3_table_offset(va)]);
> +
> + for ( ; nr--; va += PAGE_SIZE, mfn++ )
> + {
> + if ( !l1tab || !l1_table_offset(va) )
> + {
> + const l2_pgentry_t *pl2e = l2tab + l2_table_offset(va);
> +
> + if ( unlikely(!(l2e_get_flags(*pl2e) & _PAGE_PRESENT)) )
> + {
> + gprintk(XENLOG_ERR, "unable to map at VA %lx: L2e not
> present\n",
> + va);
> + ASSERT_UNREACHABLE();
> + domain_crash(d);
> +
> + break;
> + }
> +
> + unmap_domain_page(l1tab);
> + l1tab = map_l1t_from_l2e(*pl2e);
> + }
> +
> + pl1e = &l1tab[l1_table_offset(va)];
> +
> + if ( unlikely(perdomain_l1e_needs_freeing(*pl1e)) )
> + {
> + ASSERT_UNREACHABLE();
> + free_domheap_page(l1e_get_page(*pl1e));
> + }
> +
> + l1e_write(pl1e, l1e_from_mfn(*mfn, __PAGE_HYPERVISOR_RW));
> + }
> +
> + unmap_domain_page(l1tab);
> + unmap_domain_page(l2tab);
> + unmap_domain_page(l3tab);
> +}
> +
> void destroy_perdomain_mapping(struct domain *d, unsigned long va,
> unsigned int nr)
> {
> diff --git a/xen/arch/x86/smpboot.c b/xen/arch/x86/smpboot.c
> index 79a79c54c304..a740a6402272 100644
> --- a/xen/arch/x86/smpboot.c
> +++ b/xen/arch/x86/smpboot.c
> @@ -1059,8 +1059,7 @@ static int cpu_smpboot_alloc(unsigned int cpu)
> if ( gdt == NULL )
> goto out;
> per_cpu(gdt, cpu) = gdt;
> - per_cpu(gdt_l1e, cpu) =
> - l1e_from_pfn(virt_to_mfn(gdt), __PAGE_HYPERVISOR_RW);
> + per_cpu(gdt_mfn, cpu) = _mfn(virt_to_mfn(gdt));
> memcpy(gdt, boot_gdt, NR_RESERVED_GDT_PAGES * PAGE_SIZE);
> BUILD_BUG_ON(NR_CPUS > 0x10000);
> gdt[PER_CPU_GDT_ENTRY - FIRST_RESERVED_GDT_ENTRY].a = cpu;
> @@ -1069,8 +1068,7 @@ static int cpu_smpboot_alloc(unsigned int cpu)
> per_cpu(compat_gdt, cpu) = gdt = alloc_xenheap_pages(0, memflags);
> if ( gdt == NULL )
> goto out;
> - per_cpu(compat_gdt_l1e, cpu) =
> - l1e_from_pfn(virt_to_mfn(gdt), __PAGE_HYPERVISOR_RW);
> + per_cpu(compat_gdt_mfn, cpu) = _mfn(virt_to_mfn(gdt));
> memcpy(gdt, boot_compat_gdt, NR_RESERVED_GDT_PAGES * PAGE_SIZE);
> gdt[PER_CPU_GDT_ENTRY - FIRST_RESERVED_GDT_ENTRY].a = cpu;
> #endif
> diff --git a/xen/arch/x86/traps.c b/xen/arch/x86/traps.c
> index 487b8c5a78c5..a7f6fb611c34 100644
> --- a/xen/arch/x86/traps.c
> +++ b/xen/arch/x86/traps.c
> @@ -92,10 +92,10 @@ DEFINE_PER_CPU(uint64_t, efer);
> static DEFINE_PER_CPU(unsigned long, last_extable_addr);
>
> DEFINE_PER_CPU_READ_MOSTLY(seg_desc_t *, gdt);
> -DEFINE_PER_CPU_READ_MOSTLY(l1_pgentry_t, gdt_l1e);
> +DEFINE_PER_CPU_READ_MOSTLY(mfn_t, gdt_mfn);
> #ifdef CONFIG_PV32
> DEFINE_PER_CPU_READ_MOSTLY(seg_desc_t *, compat_gdt);
> -DEFINE_PER_CPU_READ_MOSTLY(l1_pgentry_t, compat_gdt_l1e);
> +DEFINE_PER_CPU_READ_MOSTLY(mfn_t, compat_gdt_mfn);
> #endif
>
> /* Master table, used by CPU0. */
> @@ -2219,11 +2219,9 @@ void __init trap_init(void)
> init_ler();
>
> /* Cache {,compat_}gdt_l1e now that physically relocation is done. */
> - this_cpu(gdt_l1e) =
> - l1e_from_pfn(virt_to_mfn(boot_gdt), __PAGE_HYPERVISOR_RW);
> + this_cpu(gdt_mfn) = _mfn(virt_to_mfn(boot_gdt));
> if ( IS_ENABLED(CONFIG_PV32) )
> - this_cpu(compat_gdt_l1e) =
> - l1e_from_pfn(virt_to_mfn(boot_compat_gdt), __PAGE_HYPERVISOR_RW);
> + this_cpu(compat_gdt_mfn) = _mfn(virt_to_mfn(boot_compat_gdt));
>
> percpu_traps_init();
>
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