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SubjectRe: [PATCH v3 4/7] x86/paravirt: remove 32-bit support from PARAVIRT_XXL
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On 07.08.20 11:39, peterz@infradead.org wrote:
> On Fri, Aug 07, 2020 at 10:38:23AM +0200, Juergen Gross wrote:
>
>> -# else
>> - const unsigned char cpu_iret[1];
>> -# endif
>> };
>>
>> static const struct patch_xxl patch_data_xxl = {
>> @@ -42,7 +38,6 @@ static const struct patch_xxl patch_data_xxl = {
>> .irq_save_fl = { 0x9c, 0x58 }, // pushf; pop %[re]ax
>> .mmu_read_cr2 = { 0x0f, 0x20, 0xd0 }, // mov %cr2, %[re]ax
>> .mmu_read_cr3 = { 0x0f, 0x20, 0xd8 }, // mov %cr3, %[re]ax
>> -# ifdef CONFIG_X86_64
>> .mmu_write_cr3 = { 0x0f, 0x22, 0xdf }, // mov %rdi, %cr3
>> .irq_restore_fl = { 0x57, 0x9d }, // push %rdi; popfq
>> .cpu_wbinvd = { 0x0f, 0x09 }, // wbinvd
>> @@ -50,19 +45,11 @@ static const struct patch_xxl patch_data_xxl = {
>> 0x48, 0x0f, 0x07 }, // swapgs; sysretq
>> .cpu_swapgs = { 0x0f, 0x01, 0xf8 }, // swapgs
>> .mov64 = { 0x48, 0x89, 0xf8 }, // mov %rdi, %rax
>> -# else
>> - .mmu_write_cr3 = { 0x0f, 0x22, 0xd8 }, // mov %eax, %cr3
>> - .irq_restore_fl = { 0x50, 0x9d }, // push %eax; popf
>> - .cpu_iret = { 0xcf }, // iret
>> -# endif
>
> I was looking at x86_64 paravirt the other day and found we actually
> have pv_ops.cpu.iret users there..

On x86_64 we have (without PARAVIRT_XXL):

#define INTERRUPT_RETURN jmp native_iret

and with PARAVIRT_XXL this is basically a jmp *pv_ops.cpu.iret which
will then be patched to either jmp native_iret or jmp xen_iret.

On x86_32 INTERRUPT_RETURN was just "iret" for the non-paravirt case.
This is the reason for above dropping of the static patch data.

> So we want to change the above to also patch iret on x86_64 or do we
> need to fix x86_64 to not have pv-iret?

We want it to stay how it is. This will let both variants (PARVIRT y/n)
continue to work.


Juergen

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