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Date: Wed, 18 Nov 2020 07:47:36 +0100
From: Jürgen Groß <jgross@...e.com>
To: Peter Zijlstra <peterz@...radead.org>
Cc: Andy Lutomirski <luto@...nel.org>,
Andrew Cooper <andrew.cooper3@...rix.com>,
Josh Poimboeuf <jpoimboe@...hat.com>,
Shinichiro Kawasaki <shinichiro.kawasaki@....com>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
Nicholas Piggin <npiggin@...il.com>,
Damien Le Moal <Damien.LeMoal@....com>,
X86 ML <x86@...nel.org>
Subject: Re: WARNING: can't access registers at asm_common_interrupt
On 16.11.20 14:04, Peter Zijlstra wrote:
> On Mon, Nov 16, 2020 at 12:56:32PM +0100, Jürgen Groß wrote:
>>>>>>>> static inline notrace unsigned long arch_local_save_flags(void)
>>>>>>>> {
>>>>>>>> PVOP_CALL_ARGS;
>>>>>>>> PVOP_TEST_NULL(irq.save_fl);
>>>>>>>> asm_inline volatile(ALTERNATIVE(paravirt_alt(PARAVIRT_CALL),
>>>>>>>> "PUSHF; POP _ASM_AX",
>>>>>>>> X86_FEATURE_NATIVE)
>>
>> I am wondering whether we really want a new feature (basically "not
>> XENPV). We could use ~X86_FEATURE_XENPV and teach apply_alternatives()
>> to understand negated features (yes, this limits the number of features
>> to 32767, but I don't think this is a real problem for quite some time).
>>
>> Thoughts?
>
> I went with the simple thing for now... If we ever want/need another
> negative alternative I suppose we can do as you suggest...
>
> I was still poking at objtool to actually dtrt though..
I'd like to include this part in my series (with a different solution
for the restore_fl part, as suggested by Andy before).
Peter, are you fine with me taking your patch and adding your SoB?
Juergen
>
> ---
> diff --git a/arch/x86/include/asm/cpufeatures.h b/arch/x86/include/asm/cpufeatures.h
> index dad350d42ecf..cc88f358bac5 100644
> --- a/arch/x86/include/asm/cpufeatures.h
> +++ b/arch/x86/include/asm/cpufeatures.h
> @@ -237,6 +237,7 @@
> #define X86_FEATURE_VMCALL ( 8*32+18) /* "" Hypervisor supports the VMCALL instruction */
> #define X86_FEATURE_VMW_VMMCALL ( 8*32+19) /* "" VMware prefers VMMCALL hypercall instruction */
> #define X86_FEATURE_SEV_ES ( 8*32+20) /* AMD Secure Encrypted Virtualization - Encrypted State */
> +#define X86_FEATURE_NOT_XENPV ( 8*32+21) /* "" inverse of X86_FEATURE_XENPV */
>
> /* Intel-defined CPU features, CPUID level 0x00000007:0 (EBX), word 9 */
> #define X86_FEATURE_FSGSBASE ( 9*32+ 0) /* RDFSBASE, WRFSBASE, RDGSBASE, WRGSBASE instructions*/
> diff --git a/arch/x86/include/asm/paravirt.h b/arch/x86/include/asm/paravirt.h
> index d25cc6830e89..e2a9d3e6b7ad 100644
> --- a/arch/x86/include/asm/paravirt.h
> +++ b/arch/x86/include/asm/paravirt.h
> @@ -645,22 +645,56 @@ bool __raw_callee_save___native_vcpu_is_preempted(long cpu);
> #ifdef CONFIG_PARAVIRT_XXL
> static inline notrace unsigned long arch_local_save_flags(void)
> {
> - return PVOP_CALLEE0(unsigned long, irq.save_fl);
> + PVOP_CALL_ARGS;
> + PVOP_TEST_NULL(irq.save_fl);
> + asm_inline volatile(ALTERNATIVE(paravirt_alt(PARAVIRT_CALL),
> + "pushf; pop %%" _ASM_AX ";",
> + X86_FEATURE_NOT_XENPV)
> + : PVOP_CALLEE_CLOBBERS, ASM_CALL_CONSTRAINT
> + : paravirt_type(irq.save_fl.func),
> + paravirt_clobber(CLBR_RET_REG)
> + : "memory", "cc");
> + return __eax;
> }
>
> static inline notrace void arch_local_irq_restore(unsigned long f)
> {
> - PVOP_VCALLEE1(irq.restore_fl, f);
> + PVOP_CALL_ARGS;
> + PVOP_TEST_NULL(irq.restore_fl);
> + asm_inline volatile(ALTERNATIVE(paravirt_alt(PARAVIRT_CALL),
> + "push %%" _ASM_ARG1 "; popf;",
> + X86_FEATURE_NOT_XENPV)
> + : PVOP_VCALLEE_CLOBBERS, ASM_CALL_CONSTRAINT
> + : paravirt_type(irq.restore_fl.func),
> + paravirt_clobber(CLBR_RET_REG),
> + PVOP_CALL_ARG1(f)
> + : "memory", "cc");
> }
>
> static inline notrace void arch_local_irq_disable(void)
> {
> - PVOP_VCALLEE0(irq.irq_disable);
> + PVOP_CALL_ARGS;
> + PVOP_TEST_NULL(irq.irq_disable);
> + asm_inline volatile(ALTERNATIVE(paravirt_alt(PARAVIRT_CALL),
> + "cli;",
> + X86_FEATURE_NOT_XENPV)
> + : PVOP_VCALLEE_CLOBBERS, ASM_CALL_CONSTRAINT
> + : paravirt_type(irq.irq_disable.func),
> + paravirt_clobber(CLBR_RET_REG)
> + : "memory", "cc");
> }
>
> static inline notrace void arch_local_irq_enable(void)
> {
> - PVOP_VCALLEE0(irq.irq_enable);
> + PVOP_CALL_ARGS;
> + PVOP_TEST_NULL(irq.irq_enable);
> + asm_inline volatile(ALTERNATIVE(paravirt_alt(PARAVIRT_CALL),
> + "sti;",
> + X86_FEATURE_NOT_XENPV)
> + : PVOP_VCALLEE_CLOBBERS, ASM_CALL_CONSTRAINT
> + : paravirt_type(irq.irq_enable.func),
> + paravirt_clobber(CLBR_RET_REG)
> + : "memory", "cc");
> }
>
> static inline notrace unsigned long arch_local_irq_save(void)
> diff --git a/arch/x86/kernel/alternative.c b/arch/x86/kernel/alternative.c
> index 2400ad62f330..5bd8f5503652 100644
> --- a/arch/x86/kernel/alternative.c
> +++ b/arch/x86/kernel/alternative.c
> @@ -723,6 +723,19 @@ void __init alternative_instructions(void)
> * patching.
> */
>
> + if (!boot_cpu_has(X86_FEATURE_XENPV))
> + setup_force_cpu_cap(X86_FEATURE_NOT_XENPV);
> +
> + /*
> + * First patch paravirt functions, such that we overwrite the indirect
> + * call with the direct call.
> + */
> + apply_paravirt(__parainstructions, __parainstructions_end);
> +
> + /*
> + * Then patch alternatives, such that those paravirt calls that are in
> + * alternatives can be overwritten by their immediate fragments.
> + */
> apply_alternatives(__alt_instructions, __alt_instructions_end);
>
> #ifdef CONFIG_SMP
> @@ -741,8 +754,6 @@ void __init alternative_instructions(void)
> }
> #endif
>
> - apply_paravirt(__parainstructions, __parainstructions_end);
> -
> restart_nmi();
> alternatives_patched = 1;
> }
> diff --git a/arch/x86/kernel/paravirt_patch.c b/arch/x86/kernel/paravirt_patch.c
> index ace6e334cb39..867498db53ad 100644
> --- a/arch/x86/kernel/paravirt_patch.c
> +++ b/arch/x86/kernel/paravirt_patch.c
> @@ -33,13 +33,9 @@ struct patch_xxl {
> };
>
> static const struct patch_xxl patch_data_xxl = {
> - .irq_irq_disable = { 0xfa }, // cli
> - .irq_irq_enable = { 0xfb }, // sti
> - .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
> .mmu_write_cr3 = { 0x0f, 0x22, 0xdf }, // mov %rdi, %cr3
> - .irq_restore_fl = { 0x57, 0x9d }, // push %rdi; popfq
> .cpu_wbinvd = { 0x0f, 0x09 }, // wbinvd
> .cpu_usergs_sysret64 = { 0x0f, 0x01, 0xf8,
> 0x48, 0x0f, 0x07 }, // swapgs; sysretq
> @@ -76,11 +72,6 @@ unsigned int native_patch(u8 type, void *insn_buff, unsigned long addr,
> switch (type) {
>
> #ifdef CONFIG_PARAVIRT_XXL
> - PATCH_CASE(irq, restore_fl, xxl, insn_buff, len);
> - PATCH_CASE(irq, save_fl, xxl, insn_buff, len);
> - PATCH_CASE(irq, irq_enable, xxl, insn_buff, len);
> - PATCH_CASE(irq, irq_disable, xxl, insn_buff, len);
> -
> PATCH_CASE(mmu, read_cr2, xxl, insn_buff, len);
> PATCH_CASE(mmu, read_cr3, xxl, insn_buff, len);
> PATCH_CASE(mmu, write_cr3, xxl, insn_buff, len);
>
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