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[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] [Xen-changelog] [xen stable-4.8] x86: slightly reduce Meltdown band-aid overhead
commit 813fe211f290843baed75aab88c2f9a249b42e68
Author: Jan Beulich <jbeulich@xxxxxxxx>
AuthorDate: Tue Mar 20 14:39:41 2018 +0100
Commit: Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Tue Mar 20 14:39:41 2018 +0100
x86: slightly reduce Meltdown band-aid overhead
I'm not sure why I didn't do this right away: By avoiding the use of
global PTEs in the cloned directmap, there's no need to fiddle with
CR4.PGE on any of the entry paths. Only the exit paths need to flush
global mappings.
The reduced flushing, however, requires that we now have interrupts off
on all entry paths until after the page table switch, so that flush IPIs
can't be serviced while on the restricted pagetables, leaving a window
where a potentially stale guest global mapping can be brought into the
TLB. Along those lines the "sync" IPI after L4 entry updates now needs
to become a real (and global) flush IPI, so that inside Xen we'll also
pick up such changes.
Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
Tested-by: Juergen Gross <jgross@xxxxxxxx>
Reviewed-by: Juergen Gross <jgross@xxxxxxxx>
Reviewed-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
x86: correct EFLAGS.IF in SYSENTER frame
Commit 9d1d31ad94 ("x86: slightly reduce Meltdown band-aid overhead")
moved the STI past the PUSHF. While this isn't an active problem (as we
force EFLAGS.IF to 1 before exiting to guest context), let's not risk
internal confusion by finding a PV guest frame with interrupts
apparently off.
Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
Acked-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
master commit: 9d1d31ad9498e6ceb285d5774e34fed5f648c273
master date: 2018-03-06 16:48:44 +0100
master commit: c4dd58f0cf23cdf119bbccedfb8c24435fc6f3ab
master date: 2018-03-16 17:27:36 +0100
---
xen/arch/x86/mm.c | 9 ++-------
xen/arch/x86/smpboot.c | 10 ++++++++++
xen/arch/x86/x86_64/compat/entry.S | 7 ++++---
xen/arch/x86/x86_64/entry.S | 23 ++++++++++++++---------
4 files changed, 30 insertions(+), 19 deletions(-)
diff --git a/xen/arch/x86/mm.c b/xen/arch/x86/mm.c
index 987ab1bb3d..78ba28b4c6 100644
--- a/xen/arch/x86/mm.c
+++ b/xen/arch/x86/mm.c
@@ -4128,14 +4128,9 @@ long do_mmu_update(
{
/*
* Force other vCPU-s of the affected guest to pick up L4 entry
- * changes (if any). Issue a flush IPI with empty operation mask to
- * facilitate this (including ourselves waiting for the IPI to
- * actually have arrived). Utilize the fact that FLUSH_VA_VALID is
- * meaningless without FLUSH_CACHE, but will allow to pass the no-op
- * check in flush_area_mask().
+ * changes (if any).
*/
- flush_area_mask(pt_owner->domain_dirty_cpumask,
- ZERO_BLOCK_PTR, FLUSH_VA_VALID);
+ flush_mask(pt_owner->domain_dirty_cpumask, FLUSH_TLB_GLOBAL);
}
perfc_add(num_page_updates, i);
diff --git a/xen/arch/x86/smpboot.c b/xen/arch/x86/smpboot.c
index e75adbe084..f40a7bdcdf 100644
--- a/xen/arch/x86/smpboot.c
+++ b/xen/arch/x86/smpboot.c
@@ -730,6 +730,7 @@ static int clone_mapping(const void *ptr, root_pgentry_t
*rpt)
}
pl1e += l1_table_offset(linear);
+ flags &= ~_PAGE_GLOBAL;
if ( l1e_get_flags(*pl1e) & _PAGE_PRESENT )
{
@@ -1036,8 +1037,17 @@ void __init smp_prepare_cpus(unsigned int max_cpus)
if ( rc )
panic("Error %d setting up PV root page table\n", rc);
if ( per_cpu(root_pgt, 0) )
+ {
get_cpu_info()->pv_cr3 = __pa(per_cpu(root_pgt, 0));
+ /*
+ * All entry points which may need to switch page tables have to start
+ * with interrupts off. Re-write what pv_trap_init() has put there.
+ */
+ _set_gate(idt_table + LEGACY_SYSCALL_VECTOR, SYS_DESC_irq_gate, 3,
+ &int80_direct_trap);
+ }
+
set_nr_sockets();
socket_cpumask = xzalloc_array(cpumask_t *, nr_sockets);
diff --git a/xen/arch/x86/x86_64/compat/entry.S
b/xen/arch/x86/x86_64/compat/entry.S
index 1c5cc9dacf..812f404771 100644
--- a/xen/arch/x86/x86_64/compat/entry.S
+++ b/xen/arch/x86/x86_64/compat/entry.S
@@ -207,7 +207,7 @@ ENTRY(compat_post_handle_exception)
/* See lstar_enter for entry register state. */
ENTRY(cstar_enter)
- sti
+ /* sti could live here when we don't switch page tables below. */
CR4_PV32_RESTORE
movq 8(%rsp),%rax /* Restore %rax. */
movq $FLAT_KERNEL_SS,8(%rsp)
@@ -227,11 +227,12 @@ ENTRY(cstar_enter)
jz .Lcstar_cr3_okay
mov %rcx, STACK_CPUINFO_FIELD(xen_cr3)(%rbx)
neg %rcx
- write_cr3 rcx, rdi, rsi
+ mov %rcx, %cr3
movq $0, STACK_CPUINFO_FIELD(xen_cr3)(%rbx)
.Lcstar_cr3_okay:
+ sti
- GET_CURRENT(bx)
+ __GET_CURRENT(bx)
movq VCPU_domain(%rbx),%rcx
cmpb $0,DOMAIN_is_32bit_pv(%rcx)
je switch_to_kernel
diff --git a/xen/arch/x86/x86_64/entry.S b/xen/arch/x86/x86_64/entry.S
index 4080da65db..c169d17159 100644
--- a/xen/arch/x86/x86_64/entry.S
+++ b/xen/arch/x86/x86_64/entry.S
@@ -148,7 +148,7 @@ UNLIKELY_END(exit_cr3)
* %ss must be saved into the space left by the trampoline.
*/
ENTRY(lstar_enter)
- sti
+ /* sti could live here when we don't switch page tables below. */
movq 8(%rsp),%rax /* Restore %rax. */
movq $FLAT_KERNEL_SS,8(%rsp)
pushq %r11
@@ -167,9 +167,10 @@ ENTRY(lstar_enter)
jz .Llstar_cr3_okay
mov %rcx, STACK_CPUINFO_FIELD(xen_cr3)(%rbx)
neg %rcx
- write_cr3 rcx, rdi, rsi
+ mov %rcx, %cr3
movq $0, STACK_CPUINFO_FIELD(xen_cr3)(%rbx)
.Llstar_cr3_okay:
+ sti
__GET_CURRENT(bx)
testb $TF_kernel_mode,VCPU_thread_flags(%rbx)
@@ -252,7 +253,7 @@ process_trap:
jmp test_all_events
ENTRY(sysenter_entry)
- sti
+ /* sti could live here when we don't switch page tables below. */
pushq $FLAT_USER_SS
pushq $0
pushfq
@@ -268,14 +269,17 @@ GLOBAL(sysenter_eflags_saved)
/* WARNING! `ret`, `call *`, `jmp *` not safe before this point. */
GET_STACK_END(bx)
+ /* PUSHF above has saved EFLAGS.IF clear (the caller had it set). */
+ orl $X86_EFLAGS_IF, UREGS_eflags(%rsp)
mov STACK_CPUINFO_FIELD(xen_cr3)(%rbx), %rcx
neg %rcx
jz .Lsyse_cr3_okay
mov %rcx, STACK_CPUINFO_FIELD(xen_cr3)(%rbx)
neg %rcx
- write_cr3 rcx, rdi, rsi
+ mov %rcx, %cr3
movq $0, STACK_CPUINFO_FIELD(xen_cr3)(%rbx)
.Lsyse_cr3_okay:
+ sti
__GET_CURRENT(bx)
cmpb $0,VCPU_sysenter_disables_events(%rbx)
@@ -322,9 +326,10 @@ ENTRY(int80_direct_trap)
jz .Lint80_cr3_okay
mov %rcx, STACK_CPUINFO_FIELD(xen_cr3)(%rbx)
neg %rcx
- write_cr3 rcx, rdi, rsi
+ mov %rcx, %cr3
movq $0, STACK_CPUINFO_FIELD(xen_cr3)(%rbx)
.Lint80_cr3_okay:
+ sti
cmpb $0,untrusted_msi(%rip)
UNLIKELY_START(ne, msi_check)
@@ -502,7 +507,7 @@ ENTRY(common_interrupt)
mov %rcx, STACK_CPUINFO_FIELD(xen_cr3)(%r14)
neg %rcx
.Lintr_cr3_load:
- write_cr3 rcx, rdi, rsi
+ mov %rcx, %cr3
xor %ecx, %ecx
mov %rcx, STACK_CPUINFO_FIELD(xen_cr3)(%r14)
testb $3, UREGS_cs(%rsp)
@@ -544,7 +549,7 @@ GLOBAL(handle_exception)
mov %rcx, STACK_CPUINFO_FIELD(xen_cr3)(%r14)
neg %rcx
.Lxcpt_cr3_load:
- write_cr3 rcx, rdi, rsi
+ mov %rcx, %cr3
xor %ecx, %ecx
mov %rcx, STACK_CPUINFO_FIELD(xen_cr3)(%r14)
testb $3, UREGS_cs(%rsp)
@@ -740,7 +745,7 @@ ENTRY(double_fault)
jns .Ldblf_cr3_load
neg %rbx
.Ldblf_cr3_load:
- write_cr3 rbx, rdi, rsi
+ mov %rbx, %cr3
.Ldblf_cr3_okay:
movq %rsp,%rdi
@@ -775,7 +780,7 @@ handle_ist_exception:
mov %rcx, STACK_CPUINFO_FIELD(xen_cr3)(%r14)
neg %rcx
.List_cr3_load:
- write_cr3 rcx, rdi, rsi
+ mov %rcx, %cr3
movq $0, STACK_CPUINFO_FIELD(xen_cr3)(%r14)
.List_cr3_okay:
--
generated by git-patchbot for /home/xen/git/xen.git#stable-4.8
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