[Xen-changelog] [xen staging] x86/suspend: Fix restoration of guest state across S3/S4

[patchbot@xxxxxxx]

commit 0c30171cb977adaf62067dfe8ddd1b283a2d7a0b
Author:     Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
AuthorDate: Wed Jun 20 15:43:57 2018 +0800
Commit:     Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
CommitDate: Wed Jul 4 12:12:14 2018 +0100

    x86/suspend: Fix restoration of guest state across S3/S4
    
    The call to freeze_domains() in enter_state() guarentees that we are
    running in idle context for the duration of S3/S4.
    
    In restore_rest_processor_state(), the stts() is problematic as it
    unilaterally sets %cr0.ts even in fully_eager FPU context.  It also fails to
    account for the non-lazy xsave state.  Luckily, these are both latent bugs, 
as
    the FPU state is corrected by the subsequent context switch away from the 
idle
    vcpu.
    
    Another aspect is that the !is_idle_vcpu(curr) paths in
    restore_rest_processor_state() are actually dead code, and removing
    these highlights that the segment saving logic is also unused.
    
    Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
    Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
---
 xen/arch/x86/acpi/suspend.c | 31 -------------------------------
 1 file changed, 31 deletions(-)

diff --git a/xen/arch/x86/acpi/suspend.c b/xen/arch/x86/acpi/suspend.c
index eecf357a9e..00e6012f54 100644
--- a/xen/arch/x86/acpi/suspend.c
+++ b/xen/arch/x86/acpi/suspend.c
@@ -18,16 +18,10 @@
 static unsigned long saved_lstar, saved_cstar;
 static unsigned long saved_sysenter_esp, saved_sysenter_eip;
 static unsigned long saved_fs_base, saved_gs_base, saved_kernel_gs_base;
-static uint16_t saved_segs[4];
 static uint64_t saved_xcr0;
 
 void save_rest_processor_state(void)
 {
-    vcpu_save_fpu(current);
-
-    asm volatile (
-        "movw %%ds,(%0); movw %%es,2(%0); movw %%fs,4(%0); movw %%gs,6(%0)"
-        : : "r" (saved_segs) : "memory" );
     saved_fs_base = rdfsbase();
     saved_gs_base = rdgsbase();
     rdmsrl(MSR_SHADOW_GS_BASE, saved_kernel_gs_base);
@@ -46,8 +40,6 @@ void save_rest_processor_state(void)
 
 void restore_rest_processor_state(void)
 {
-    struct vcpu *curr = current;
-
     load_TR();
 
     /* Recover syscall MSRs */
@@ -69,32 +61,9 @@ void restore_rest_processor_state(void)
         wrmsr(MSR_IA32_SYSENTER_CS, __HYPERVISOR_CS, 0);
     }
 
-    if ( !is_idle_vcpu(curr) )
-    {
-        asm volatile (
-            "movw (%0),%%ds; movw 2(%0),%%es; movw 4(%0),%%fs"
-            : : "r" (saved_segs) : "memory" );
-        do_set_segment_base(SEGBASE_GS_USER_SEL, saved_segs[3]);
-    }
-
     if ( cpu_has_xsave && !set_xcr0(saved_xcr0) )
         BUG();
 
-    /* Maybe load the debug registers. */
-    BUG_ON(!is_pv_vcpu(curr));
-    if ( !is_idle_vcpu(curr) && curr->arch.debugreg[7] )
-    {
-        write_debugreg(0, curr->arch.debugreg[0]);
-        write_debugreg(1, curr->arch.debugreg[1]);
-        write_debugreg(2, curr->arch.debugreg[2]);
-        write_debugreg(3, curr->arch.debugreg[3]);
-        write_debugreg(6, curr->arch.debugreg[6]);
-        write_debugreg(7, curr->arch.debugreg[7]);
-    }
-
-    /* Reload FPU state on next FPU use. */
-    stts();
-
     wrmsrl(MSR_IA32_CR_PAT, XEN_MSR_PAT);
 
     mtrr_bp_restore();
--
generated by git-patchbot for /home/xen/git/xen.git#staging

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