Messages in this thread | | | Date | Sat, 9 Nov 2019 00:45:47 +0100 (CET) | From | Thomas Gleixner <> | Subject | Re: [patch 4/9] x86/io: Speedup schedule out of I/O bitmap user |
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On Fri, 8 Nov 2019, Andy Lutomirski wrote: > On 11/7/19 6:08 AM, Thomas Gleixner wrote: > > On Thu, 7 Nov 2019, Thomas Gleixner wrote: > >> Just that I can't add the storage to tss_struct due to the VMX insanity of > >> setting TSS limit hard to 0x67 on vmexit instead of restoring the host > >> value. > > > > Well, I can. The build bugon in vmx.c is just bogus. > > SDM vol 3 27.5.2 says the BUILD_BUG_ON is right. Or am I > misunderstanding you? > > I'm reasonably confident that the TSS limit is indeed 0x67 after VM > exit, and I wrote the existing code that tries to optimize this to avoid > LTR when not needed.
The BUILD_BUG_ON(IO_BITMAP_OFFSET - 1 == 0x67) in the VMX code is bogus in two aspects:
1) This wants to be in generic x86 code
2) The IO_BITMAP_OFFSET is not the right thing to check because it makes asssumptions about the layout of tss_struct. Nothing requires that the I/O bitmap is placed right after x86_tss, which is the hardware mandated tss structure. It pointlessly makes restrictions on the struct tss_struct layout.
The proper thing to check is:
- Offset of x86_tss in tss_struct is 0 - Size of x86_tss == 0x68
We already have the page alignment sanity check off TSS in cpu_entry_area.c. That's where this should have gone into in the first place.
Thanks,
tglx
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