Re: [PATCH 10/22] x86/traps: Move subarch_percpu_traps_init() into traps-setup.c

[Jan Beulich <jbeulich@xxxxxxxx>]

On 11.08.2025 10:17, Andrew Cooper wrote:
> On 08/08/2025 9:23 pm, Andrew Cooper wrote:
>> ... along with the supporting functions.  Switch to Xen coding style, and 
>> make
>> static as there are no external callers.
>>
>> Rename to legacy_syscall_init() as a more accurate name.
>>
>> No functional change.
>>
>> Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
>> ---
>> CC: Jan Beulich <JBeulich@xxxxxxxx>
>> CC: Roger Pau Monné <roger.pau@xxxxxxxxxx>
>> ---
>>  xen/arch/x86/include/asm/system.h |  2 -
>>  xen/arch/x86/traps-setup.c        | 97 ++++++++++++++++++++++++++++++-
>>  xen/arch/x86/x86_64/traps.c       | 92 -----------------------------
>>  3 files changed, 95 insertions(+), 96 deletions(-)
>>
>> diff --git a/xen/arch/x86/include/asm/system.h 
>> b/xen/arch/x86/include/asm/system.h
>> index 3cdc56e4ba6d..6c2800d8158d 100644
>> --- a/xen/arch/x86/include/asm/system.h
>> +++ b/xen/arch/x86/include/asm/system.h
>> @@ -256,6 +256,4 @@ static inline int local_irq_is_enabled(void)
>>  #define BROKEN_ACPI_Sx          0x0001
>>  #define BROKEN_INIT_AFTER_S1    0x0002
>>  
>> -void subarch_percpu_traps_init(void);
>> -
>>  #endif
>> diff --git a/xen/arch/x86/traps-setup.c b/xen/arch/x86/traps-setup.c
>> index 13b8fcf0ba51..fbae7072c292 100644
>> --- a/xen/arch/x86/traps-setup.c
>> +++ b/xen/arch/x86/traps-setup.c
>> @@ -2,13 +2,15 @@
>>  /*
>>   * Configuration of event handling for all CPUs.
>>   */
>> +#include <xen/domain_page.h>
>>  #include <xen/init.h>
>>  #include <xen/param.h>
>>  
>> +#include <asm/endbr.h>
>>  #include <asm/idt.h>
>>  #include <asm/msr.h>
>>  #include <asm/shstk.h>
>> -#include <asm/system.h>
>> +#include <asm/stubs.h>
>>  #include <asm/traps.h>
>>  
>>  DEFINE_PER_CPU_READ_MOSTLY(idt_entry_t *, idt);
>> @@ -19,6 +21,8 @@ static bool __initdata opt_ler;
>>  boolean_param("ler", opt_ler);
>>  
>>  void nocall entry_PF(void);
>> +void nocall lstar_enter(void);
>> +void nocall cstar_enter(void);
>>  
>>  /*
>>   * Sets up system tables and descriptors for IDT devliery.
>> @@ -138,6 +142,95 @@ static void load_system_tables(void)
>>      BUG_ON(stack_bottom & 15);
>>  }
>>  
>> +static unsigned int write_stub_trampoline(
>> +    unsigned char *stub, unsigned long stub_va,
>> +    unsigned long stack_bottom, unsigned long target_va)
>> +{
>> +    unsigned char *p = stub;
>> +
>> +    if ( cpu_has_xen_ibt )
>> +    {
>> +        place_endbr64(p);
>> +        p += 4;
>> +    }
>> +
>> +    /* Store guest %rax into %ss slot */
>> +    /* movabsq %rax, stack_bottom - 8 */
>> +    *p++ = 0x48;
>> +    *p++ = 0xa3;
>> +    *(uint64_t *)p = stack_bottom - 8;
>> +    p += 8;
>> +
>> +    /* Store guest %rsp in %rax */
>> +    /* movq %rsp, %rax */
>> +    *p++ = 0x48;
>> +    *p++ = 0x89;
>> +    *p++ = 0xe0;
>> +
>> +    /* Switch to Xen stack */
>> +    /* movabsq $stack_bottom - 8, %rsp */
>> +    *p++ = 0x48;
>> +    *p++ = 0xbc;
>> +    *(uint64_t *)p = stack_bottom - 8;
>> +    p += 8;
>> +
>> +    /* jmp target_va */
>> +    *p++ = 0xe9;
>> +    *(int32_t *)p = target_va - (stub_va + (p - stub) + 4);
>> +    p += 4;
>> +
>> +    /* Round up to a multiple of 16 bytes. */
>> +    return ROUNDUP(p - stub, 16);
>> +}
>> +
>> +static void legacy_syscall_init(void)
>> +{
>> +    unsigned long stack_bottom = get_stack_bottom();
>> +    unsigned long stub_va = this_cpu(stubs.addr);
>> +    unsigned char *stub_page;
>> +    unsigned int offset;
>> +
>> +    /* No PV guests?  No need to set up SYSCALL/SYSENTER infrastructure. */
>> +    if ( !IS_ENABLED(CONFIG_PV) )
>> +        return;
>> +
>> +    stub_page = map_domain_page(_mfn(this_cpu(stubs.mfn)));
>> +
>> +    /*
>> +     * Trampoline for SYSCALL entry from 64-bit mode.  The VT-x HVM vcpu
>> +     * context switch logic relies on the SYSCALL trampoline being at the
>> +     * start of the stubs.
>> +     */
>> +    wrmsrl(MSR_LSTAR, stub_va);
>> +    offset = write_stub_trampoline(stub_page + (stub_va & ~PAGE_MASK),
>> +                                   stub_va, stack_bottom,
>> +                                   (unsigned long)lstar_enter);
>> +    stub_va += offset;
>> +
>> +    if ( cpu_has_sep )
>> +    {
>> +        /* SYSENTER entry. */
>> +        wrmsrl(MSR_IA32_SYSENTER_ESP, stack_bottom);
>> +        wrmsrl(MSR_IA32_SYSENTER_EIP, (unsigned long)sysenter_entry);
>> +        wrmsr(MSR_IA32_SYSENTER_CS, __HYPERVISOR_CS, 0);
>> +    }
>> +
>> +    /* Trampoline for SYSCALL entry from compatibility mode. */
>> +    wrmsrl(MSR_CSTAR, stub_va);
>> +    offset += write_stub_trampoline(stub_page + (stub_va & ~PAGE_MASK),
>> +                                    stub_va, stack_bottom,
>> +                                    (unsigned long)cstar_enter);
>> +
>> +    /* Don't consume more than half of the stub space here. */
>> +    ASSERT(offset <= STUB_BUF_SIZE / 2);
>> +
>> +    unmap_domain_page(stub_page);
>> +
>> +    /* Common SYSCALL parameters. */
>> +    wrmsrl(MSR_STAR, XEN_MSR_STAR);
>> +    wrmsrl(MSR_SYSCALL_MASK, XEN_SYSCALL_MASK);
>> +}
> 
> These want adjusting to use wrmsrns(), similarly to the previous patch. 
> Fixed locally.

Also the one higher in the function, I suppose.

Acked-by: Jan Beulich <jbeulich@xxxxxxxx>

Jan