Messages in this thread | | | Date | Sun, 1 Oct 2023 20:40:30 +1100 | Subject | Re: [PATCH kernel v2] x86/compressed/64: reduce #VC nesting for intercepted CPUID for SEV-SNP guest | From | Alexey Kardashevskiy <> |
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On 30/9/23 17:17, Borislav Petkov wrote: > 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.
Ingo says different, who wins? :)
> Then, it should be defined only in sev-shared.c for now.
sev-shared.c makes me sad. Including .c is not ... nice, I would avoid adding stuff to it at any cost.
> 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.
What is "prot" going to signify?
And what about Tom's "x86/sev: Fix SNP CPUID requests to the hypervisor", are you taking that one or I have to repost this one and the Tom's patch?
-- Alexey
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