From: "Liu, Jing2" <jing2.liu@linux.intel.com>
To: Sean Christopherson <seanjc@google.com>
Cc: pbonzini@redhat.com, kvm@vger.kernel.org,
linux-kernel@vger.kernel.org, jing2.liu@intel.com
Subject: Re: [PATCH RFC 4/7] kvm: x86: Add new ioctls for XSAVE extension
Date: Wed, 26 May 2021 14:09:03 +0800 [thread overview]
Message-ID: <920df897-56d8-1f81-7ce2-0050fb744bd7@linux.intel.com> (raw)
In-Reply-To: <YKwfsIT5DuE+L+4M@google.com>
On 5/25/2021 5:50 AM, Sean Christopherson wrote:
> On Sun, Feb 07, 2021, Jing Liu wrote:
>> The static xstate buffer kvm_xsave contains the extended register
>> states, but it is not enough for dynamic features with large state.
>>
>> Introduce a new capability called KVM_CAP_X86_XSAVE_EXTENSION to
>> detect if hardware has XSAVE extension (XFD). Meanwhile, add two
>> new ioctl interfaces to get/set the whole xstate using struct
>> kvm_xsave_extension buffer containing both static and dynamic
>> xfeatures. Reuse fill_xsave and load_xsave for both cases.
>>
>> Signed-off-by: Jing Liu <jing2.liu@linux.intel.com>
>> ---
>> arch/x86/include/uapi/asm/kvm.h | 5 +++
>> arch/x86/kvm/x86.c | 70 +++++++++++++++++++++++++--------
>> include/uapi/linux/kvm.h | 8 ++++
>> 3 files changed, 66 insertions(+), 17 deletions(-)
>>
>> diff --git a/arch/x86/include/uapi/asm/kvm.h b/arch/x86/include/uapi/asm/kvm.h
>> index 89e5f3d1bba8..bf785e89a728 100644
>> --- a/arch/x86/include/uapi/asm/kvm.h
>> +++ b/arch/x86/include/uapi/asm/kvm.h
>> @@ -362,6 +362,11 @@ struct kvm_xsave {
>> __u32 region[1024];
>> };
>>
>> +/* for KVM_CAP_XSAVE_EXTENSION */
>> +struct kvm_xsave_extension {
>> + __u32 region[3072];
> Fool me once, shame on you (Intel). Fool me twice, shame on me (KVM).
>
> As amusing as kvm_xsave_really_extended would be, the required size should be
> discoverable, not hardcoded.
Thanks for reviewing the patch.
When looking at current kvm_xsave structure, I felt confusing about the
static
hardcoding of 1024 bytes, but failed to find clue for its final decision
in 2010[1].
So we'd prefer to changing the way right? Please correct me if I
misunderstood.
> Nothing prevents a hardware vendor from inventing
> a newfangled feature that requires yet more space.
> As an alternative to adding a dedicated capability, can we leverage
> GET_SUPPORTED_CPUID, leaf CPUID.0xD,
Yes, this is a good way to avoid a dedicated capability. Thanks for the
suggestion.
Use 0xD.1.EBX for size of enabled xcr0|xss if supposing kvm_xsave cares
both.
> to enumerate the minimum required size and
> state
For the state, an extreme case is using an old qemu as follows, but a
new kvm with more future_featureZ supported. If hardware vendor arranges
one by one, it's OK to use static state like X86XSaveArea(2) and
get/set between userspace and kvm because it's non-compacted. If not,
the state will not correct.
So far it is OK, so I'm wondering if this would be an issue for now?
X86XSaveArea2 {
...
XSaveAVX
...
AMX_XTILE;
future_featureX;
future_featureY;
}
> that the new ioctl() is available if the min size is greater than 1024?
> Or is that unnecessarily convoluted...
To enable a dynamic size kvm_xsave2(Thanks Jim's name suggestion), if
things as
follows are what we might want.
/* for xstate large than 1024 */
struct kvm_xsave2 {
int size; // size of the whole xstate
void *ptr; // xstate pointer
}
#define KVM_GET_XSAVE2 _IOW(KVMIO, 0xa4, struct kvm_xsave2)
Take @size together, so KVM need not fetch 0xd.1.ebx each time or a
dedicated
variable.
For Userspace(Qemu):
struct X86XSaveArea2 {...}// new struct holding all features
if 0xd.1.ebx <= sizeof(kvm_xsave)
env->xsave_buf = alloc(sizeof(kvm_xsave))
...
ioctl(KVM_GET/SET_XSAVE, X86XSaveArea *)
else
env->xsave_buf = alloc(0xd.1.ebx + sizeof(int))
...
xsave2 = env->xsave_buf
xsave2->size = ...
X86XSaveArea2 *area2 = xsave2->ptr
ioctl(KVM_GET/SET_XSAVE2, xsave2)
endif
[1] https://lore.kernel.org/kvm/4C10AE1D.40604@redhat.com/
Thanks,
Jing
next prev parent reply other threads:[~2021-05-26 6:09 UTC|newest]
Thread overview: 39+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-02-07 15:42 [PATCH RFC 0/7] Introduce support for guest AMX feature Jing Liu
2021-02-07 15:42 ` [PATCH RFC 1/7] kvm: x86: Expose XFD CPUID to guest Jing Liu
2021-05-24 21:34 ` Sean Christopherson
2021-06-07 3:27 ` Liu, Jing2
2021-02-07 15:42 ` [PATCH RFC 2/7] kvm: x86: Introduce XFD MSRs as passthrough " Jing Liu
2021-05-24 21:43 ` Sean Christopherson
2021-05-24 21:57 ` Jim Mattson
2021-06-02 3:12 ` Liu, Jing2
2021-06-23 17:50 ` Dave Hansen
2021-06-28 2:00 ` Liu, Jing2
2021-06-29 17:58 ` Dave Hansen
2021-07-06 7:33 ` Liu, Jing2
2021-02-07 15:42 ` [PATCH RFC 3/7] kvm: x86: XSAVE state and XFD MSRs context switch Jing Liu
2021-02-07 11:49 ` Borislav Petkov
2021-02-08 3:35 ` Liu, Jing2
2021-02-08 10:25 ` Paolo Bonzini
2021-02-08 17:31 ` Sean Christopherson
2021-02-08 17:45 ` Paolo Bonzini
2021-02-08 18:04 ` Sean Christopherson
2021-02-08 18:12 ` Paolo Bonzini
2021-02-08 18:55 ` Konrad Rzeszutek Wilk
2021-02-22 8:51 ` Liu, Jing2
2021-02-22 8:36 ` Liu, Jing2
2021-02-07 15:42 ` [PATCH RFC 4/7] kvm: x86: Add new ioctls for XSAVE extension Jing Liu
2021-05-24 21:50 ` Sean Christopherson
2021-05-26 6:09 ` Liu, Jing2 [this message]
2021-05-26 14:43 ` Sean Christopherson
2021-06-01 10:24 ` Liu, Jing2
2021-06-07 5:23 ` Liu, Jing2
2021-05-24 22:06 ` Jim Mattson
2021-05-26 6:11 ` Liu, Jing2
2021-02-07 15:42 ` [PATCH RFC 5/7] kvm: x86: Revise CPUID.D.1.EBX for alignment rule Jing Liu
2021-05-24 21:28 ` Sean Christopherson
2021-06-03 4:45 ` Liu, Jing2
2021-02-07 15:42 ` [PATCH RFC 6/7] kvm: x86: Add AMX_TILE, AMX_INT8 and AMX_BF16 support Jing Liu
2021-02-07 15:42 ` [PATCH RFC 7/7] kvm: x86: AMX XCR0 support for guest Jing Liu
2021-05-24 21:53 ` Sean Christopherson
2021-05-26 7:54 ` Liu, Jing2
2021-05-26 14:54 ` Sean Christopherson
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