Messages in this thread | | | Date | Sat, 30 Sep 2023 09:17:59 +0200 | From | Borislav Petkov <> | Subject | Re: [PATCH kernel v2] x86/compressed/64: reduce #VC nesting for intercepted CPUID for SEV-SNP guest |
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On Tue, Sep 26, 2023 at 02:05:26PM +1000, Alexey Kardashevskiy wrote: > vc_raw_handle_exception #1: exit_code 72 (CPUID) eax d ecx 1 > We lock the main GHCB and while it is locked we get to
Please use passive voice in your commit message: no "we" or "I", etc, and describe your changes in imperative mood.
Also, pls read section "2) Describe your changes" in Documentation/process/submitting-patches.rst for more details.
Also, see section "Changelog" in Documentation/process/maintainer-tip.rst
Bottom line is: personal pronouns are ambiguous in text, especially with so many parties/companies/etc developing the kernel so let's avoid them please.
> snp_cpuid_postprocess() which executes "rdmsr" of MSR_IA32_XSS==0xda0 which > triggers: > > vc_raw_handle_exception #2: exit_code 7c (MSR) ecx da0 > Here we lock the backup ghcb. > > And then PMC NMI comes which cannot complete as there is no GHCB page left > to use: > > CPU: 5 PID: 566 Comm: touch Not tainted 6.5.0-rc2-aik-ad9c-g7413e71d3dcf-dirty #27 > Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS unknown unknown > Call Trace: > <NMI> > dump_stack_lvl+0x44/0x60 > panic+0x222/0x310 > ____sev_get_ghcb+0x21e/0x220 > __sev_es_nmi_complete+0x28/0xf0 > exc_nmi+0x1ac/0x1c0 > end_repeat_nmi+0x16/0x67 > ... > </NMI> > <TASK> > vc_raw_handle_exception+0x9e/0x2c0 > kernel_exc_vmm_communication+0x4d/0xa0 > asm_exc_vmm_communication+0x31/0x60 > RIP: 0010:snp_cpuid+0x2ad/0x420
Drop that splat like we talked.
> +/* Paravirt SEV-ES rdmsr which avoids extra #VC event */ > +#define rdmsr_safe_GHCB(msr, low, high, ghcb, ctxt) ({ \ > + int __ret; \ > + \ > + ghcb_set_rcx((ghcb), (msr)); \ > + __ret = sev_es_ghcb_hv_call((ghcb), (ctxt), SVM_EXIT_MSR, 0, 0); \ > + if (__ret == ES_OK) { \ > + low = (ghcb)->save.rax; \ > + high = (ghcb)->save.rdx; \ > + /* Invalidate qwords for likely another following GHCB call */ \ > + vc_ghcb_invalidate(ghcb); \ > + } \ > + __ret; }) > +
First of all, this should be a function, not a macro.
Then, it should be defined only in sev-shared.c for now.
Furthermore, it should not be called "rdmsr" or so but something like
ghcb_prot_read_msr()
or so to denote that it is using the GHCB protocol to read the MSR. I'm sure it'll gain more users with time.
Thx.
-- Regards/Gruss, Boris.
https://people.kernel.org/tglx/notes-about-netiquette
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