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Subject: Re: [patch 05/15] x86/tlb: Move __flush_tlb() out of line
To:     Tom Lendacky <thomas.lendacky@amd.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        LKML <linux-kernel@vger.kernel.org>
Cc:     x86@kernel.org, Kees Cook <keescook@chromium.org>,
        Paolo Bonzini <pbonzini@redhat.com>,
        Boris Ostrovsky <boris.ostrovsky@oracle.com>
References: <20200419203137.214111265@linutronix.de>
 <20200419203336.134117165@linutronix.de>
 <5857df01-abeb-c6cd-8e92-64eb365dc835@amd.com>
 <fab4e80a-3df2-a177-c5fe-1ab995953727@suse.com>
 <852c1af7-bc1c-a86c-d390-7547563bdde4@amd.com>
From:   =?UTF-8?B?SsO8cmdlbiBHcm/Dnw==?= <jgross@suse.com>
Message-ID: <76124c5d-d5ab-6ad0-b24b-4127894107e5@suse.com>
Date:   Mon, 20 Apr 2020 16:38:17 +0200
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On 20.04.20 16:26, Tom Lendacky wrote:
> On 4/20/20 9:03 AM, Jürgen Groß wrote:
>> On 20.04.20 15:48, Tom Lendacky wrote:
>>> On 4/19/20 3:31 PM, Thomas Gleixner wrote:
>>>> cpu_tlbstate is exported because various TLB related functions need 
>>>> access
>>>> to it, but cpu_tlbstate is sensitive information which should only be
>>>> accessed by well contained kernel functions and not be directly 
>>>> exposed to
>>>> modules.
>>>>
>>>> The various TLB flush functions need access to cpu_tlbstate. As a first
>>>> step move __flush_tlb() out of line and hide the native function. The
>>>> latter can be static when CONFIG_PARAVIRT is disabled.
>>>>
>>>> Consolidate the name space while at it and remove the pointless extra
>>>> wrapper in the paravirt code.
>>>>
>>>> No functional change.
>>>>
>>>> Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
>>>> Cc: Thomas Lendacky <Thomas.Lendacky@amd.com>
>>>> Cc: Juergen Gross <jgross@suse.com>
>>>> ---
>>>>   arch/x86/include/asm/paravirt.h    |    4 +++-
>>>>   arch/x86/include/asm/tlbflush.h    |   29 
>>>> +++++------------------------
>>>>   arch/x86/kernel/cpu/mtrr/generic.c |    4 ++--
>>>>   arch/x86/kernel/paravirt.c         |    7 +------
>>>>   arch/x86/mm/mem_encrypt.c          |    2 +-
>>>>   arch/x86/mm/tlb.c                  |   33 
>>>> ++++++++++++++++++++++++++++++++-
>>>>   arch/x86/platform/uv/tlb_uv.c      |    2 +-
>>>>   7 files changed, 45 insertions(+), 36 deletions(-)
>>>>
>>>> --- a/arch/x86/include/asm/paravirt.h
>>>> +++ b/arch/x86/include/asm/paravirt.h
>>>> @@ -47,7 +47,9 @@ static inline void slow_down_io(void)
>>>>   #endif
>>>>   }
>>>> -static inline void __flush_tlb(void)
>>>> +void native_flush_tlb_local(void);
>>>> +
>>>> +static inline void __flush_tlb_local(void)
>>>>   {
>>>>       PVOP_VCALL0(mmu.flush_tlb_user);
>>>>   }
>>>> --- a/arch/x86/include/asm/tlbflush.h
>>>> +++ b/arch/x86/include/asm/tlbflush.h
>>>> @@ -140,12 +140,13 @@ static inline unsigned long build_cr3_no
>>>>       return __sme_pa(pgd) | kern_pcid(asid) | CR3_NOFLUSH;
>>>>   }
>>>> +void flush_tlb_local(void);
>>>> +
>>>>   #ifdef CONFIG_PARAVIRT
>>>>   #include <asm/paravirt.h>
>>>>   #else
>>>> -#define __flush_tlb() __native_flush_tlb()
>>>> -#define __flush_tlb_global() __native_flush_tlb_global()
>>>> -#define __flush_tlb_one_user(addr) __native_flush_tlb_one_user(addr)
>>>> +#define __flush_tlb_global()        __native_flush_tlb_global()
>>>> +#define __flush_tlb_one_user(addr)    
>>>> __native_flush_tlb_one_user(addr)
>>>>   #endif
>>>>   struct tlb_context {
>>>> @@ -371,24 +372,6 @@ static inline void invalidate_user_asid(
>>>>   }
>>>>   /*
>>>> - * flush the entire current user mapping
>>>> - */
>>>> -static inline void __native_flush_tlb(void)
>>>> -{
>>>> -    /*
>>>> -     * Preemption or interrupts must be disabled to protect the access
>>>> -     * to the per CPU variable and to prevent being preempted between
>>>> -     * read_cr3() and write_cr3().
>>>> -     */
>>>> -    WARN_ON_ONCE(preemptible());
>>>> -
>>>> -    invalidate_user_asid(this_cpu_read(cpu_tlbstate.loaded_mm_asid));
>>>> -
>>>> -    /* If current->mm == NULL then the read_cr3() "borrows" an mm */
>>>> -    native_write_cr3(__native_read_cr3());
>>>> -}
>>>> -
>>>> -/*
>>>>    * flush everything
>>>>    */
>>>>   static inline void __native_flush_tlb_global(void)
>>>> @@ -461,7 +444,7 @@ static inline void __flush_tlb_all(void)
>>>>           /*
>>>>            * !PGE -> !PCID (setup_pcid()), thus every flush is total.
>>>>            */
>>>> -        __flush_tlb();
>>>> +        flush_tlb_local();
>>>>       }
>>>>   }
>>>> @@ -537,8 +520,6 @@ struct flush_tlb_info {
>>>>       bool            freed_tables;
>>>>   };
>>>> -#define local_flush_tlb() __flush_tlb()
>>>> -
>>>>   #define flush_tlb_mm(mm)                        \
>>>>           flush_tlb_mm_range(mm, 0UL, TLB_FLUSH_ALL, 0UL, true)
>>>> --- a/arch/x86/kernel/cpu/mtrr/generic.c
>>>> +++ b/arch/x86/kernel/cpu/mtrr/generic.c
>>>> @@ -761,7 +761,7 @@ static void prepare_set(void) __acquires
>>>>       /* Flush all TLBs via a mov %cr3, %reg; mov %reg, %cr3 */
>>>>       count_vm_tlb_event(NR_TLB_LOCAL_FLUSH_ALL);
>>>> -    __flush_tlb();
>>>> +    flush_tlb_local();
>>>>       /* Save MTRR state */
>>>>       rdmsr(MSR_MTRRdefType, deftype_lo, deftype_hi);
>>>> @@ -778,7 +778,7 @@ static void post_set(void) __releases(se
>>>>   {
>>>>       /* Flush TLBs (no need to flush caches - they are disabled) */
>>>>       count_vm_tlb_event(NR_TLB_LOCAL_FLUSH_ALL);
>>>> -    __flush_tlb();
>>>> +    flush_tlb_local();
>>>>       /* Intel (P6) standard MTRRs */
>>>>       mtrr_wrmsr(MSR_MTRRdefType, deftype_lo, deftype_hi);
>>>> --- a/arch/x86/kernel/paravirt.c
>>>> +++ b/arch/x86/kernel/paravirt.c
>>>> @@ -160,11 +160,6 @@ unsigned paravirt_patch_insns(void *insn
>>>>       return insn_len;
>>>>   }
>>>> -static void native_flush_tlb(void)
>>>> -{
>>>> -    __native_flush_tlb();
>>>> -}
>>>> -
>>>>   /*
>>>>    * Global pages have to be flushed a bit differently. Not a real
>>>>    * performance problem because this does not happen often.
>>>> @@ -359,7 +354,7 @@ struct paravirt_patch_template pv_ops =
>>>>   #endif /* CONFIG_PARAVIRT_XXL */
>>>>       /* Mmu ops. */
>>>> -    .mmu.flush_tlb_user    = native_flush_tlb,
>>>> +    .mmu.flush_tlb_user    = native_flush_tlb_local,
>>>>       .mmu.flush_tlb_kernel    = native_flush_tlb_global,
>>>>       .mmu.flush_tlb_one_user    = native_flush_tlb_one_user,
>>>>       .mmu.flush_tlb_others    = native_flush_tlb_others,
>>>> --- a/arch/x86/mm/mem_encrypt.c
>>>> +++ b/arch/x86/mm/mem_encrypt.c
>>>> @@ -134,7 +134,7 @@ static void __init __sme_early_map_unmap
>>>>           size = (size <= PMD_SIZE) ? 0 : size - PMD_SIZE;
>>>>       } while (size);
>>>> -    __native_flush_tlb();
>>>> +    flush_tlb_local();
>>>
>>> This invoked __native_flush_tlb() because of how early it is called 
>>> and the paravirt ops support isn't set up yet, resulting in a crash 
>>> if not invoking the native version directly. So this needs a "native" 
>>> version of the tlb flush to invoke.
>>
>> I don't think this is still true. With my rework of pvops to have all
>> functions in one struct which is initialized statically initially
>> everything should work from the time the kernel is mapped.
>>
>> In case it doesn't there is something very wrong IMO.
> 
> The memory encryption support was implemented in 4.14, so it's quite 
> possible that this isn't an issue now. I'll test out the patch and 
> verify it. What release did your pvops rework land in?

4.20.


Juergen