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Message-ID: <20210401103208.GA28954@zn.tnic>
Date: Thu, 1 Apr 2021 12:32:08 +0200
From: Borislav Petkov <bp@...en8.de>
To: Brijesh Singh <brijesh.singh@....com>
Cc: linux-kernel@...r.kernel.org, x86@...nel.org, kvm@...r.kernel.org,
ak@...ux.intel.com, Thomas Gleixner <tglx@...utronix.de>,
Ingo Molnar <mingo@...hat.com>, Joerg Roedel <jroedel@...e.de>,
"H. Peter Anvin" <hpa@...or.com>, Tony Luck <tony.luck@...el.com>,
Dave Hansen <dave.hansen@...el.com>,
"Peter Zijlstra (Intel)" <peterz@...radead.org>,
Paolo Bonzini <pbonzini@...hat.com>,
Tom Lendacky <thomas.lendacky@....com>,
David Rientjes <rientjes@...gle.com>,
Sean Christopherson <seanjc@...gle.com>
Subject: Re: [RFC Part1 PATCH 04/13] x86/sev-snp: define page state change
VMGEXIT structure
On Wed, Mar 24, 2021 at 11:44:15AM -0500, Brijesh Singh wrote:
> An SNP-active guest will use the page state change VNAE MGEXIT defined in
I guess this was supposed to mean "NAE VMGEXIT" but pls write "NAE" out
at least once so that reader can find its way around the spec.
> the GHCB specification section 4.1.6 to ask the hypervisor to make the
> guest page private or shared in the RMP table. In addition to the
> private/shared, the guest can also ask the hypervisor to split or
> combine multiple 4K validated pages as a single 2M page or vice versa.
>
> Cc: Thomas Gleixner <tglx@...utronix.de>
> Cc: Ingo Molnar <mingo@...hat.com>
> Cc: Borislav Petkov <bp@...en8.de>
> Cc: Joerg Roedel <jroedel@...e.de>
> Cc: "H. Peter Anvin" <hpa@...or.com>
> Cc: Tony Luck <tony.luck@...el.com>
> Cc: Dave Hansen <dave.hansen@...el.com>
> Cc: "Peter Zijlstra (Intel)" <peterz@...radead.org>
> Cc: Paolo Bonzini <pbonzini@...hat.com>
> Cc: Tom Lendacky <thomas.lendacky@....com>
> Cc: David Rientjes <rientjes@...gle.com>
> Cc: Sean Christopherson <seanjc@...gle.com>
> Cc: x86@...nel.org
> Cc: kvm@...r.kernel.org
> Signed-off-by: Brijesh Singh <brijesh.singh@....com>
> ---
> arch/x86/include/asm/sev-snp.h | 34 +++++++++++++++++++++++++++++++++
> arch/x86/include/uapi/asm/svm.h | 1 +
> 2 files changed, 35 insertions(+)
>
> diff --git a/arch/x86/include/asm/sev-snp.h b/arch/x86/include/asm/sev-snp.h
> index 5a6d1367cab7..f514dad276f2 100644
> --- a/arch/x86/include/asm/sev-snp.h
> +++ b/arch/x86/include/asm/sev-snp.h
> @@ -22,6 +22,40 @@
> #define RMP_PG_SIZE_2M 1
> #define RMP_PG_SIZE_4K 0
>
> +/* Page State Change MSR Protocol */
> +#define GHCB_SNP_PAGE_STATE_CHANGE_REQ 0x0014
> +#define GHCB_SNP_PAGE_STATE_REQ_GFN(v, o) (GHCB_SNP_PAGE_STATE_CHANGE_REQ | \
> + ((unsigned long)((o) & 0xf) << 52) | \
> + (((v) << 12) & 0xffffffffffffff))
This macro needs to be more readable and I'm not sure the masking is
correct. IOW, something like this perhaps:
#define GHCB_SNP_PAGE_STATE_REQ_GFN(va, operation) \
((((operation) & 0xf) << 52) | ((va) & GENMASK_ULL(51, 12)) | GHCB_SNP_PAGE_STATE_CHANGE_REQ)
where you have each GHCBData element at the proper place, msb to lsb.
Now, GHCB spec says:
"GHCBData[51:12] – Guest physical frame number"
and I'm not clear as to what this macro takes: a virtual address or a
pfn. If it is a pfn, then you need to do:
(((pfn) << 12) & GENMASK_ULL(51, 0))
but if it is a virtual address you need to do what I have above. Since
you do "<< 12" then it must be a pfn already but then you should call
the argument "pfn" so that it is clear what it takes.
Your mask above covers [55:0] but [55:52] is the page operation so the
high bit in that mask needs to be 51.
AFAICT, ofc.
> +#define SNP_PAGE_STATE_PRIVATE 1
> +#define SNP_PAGE_STATE_SHARED 2
> +#define SNP_PAGE_STATE_PSMASH 3
> +#define SNP_PAGE_STATE_UNSMASH 4
> +
> +#define GHCB_SNP_PAGE_STATE_CHANGE_RESP 0x0015
> +#define GHCB_SNP_PAGE_STATE_RESP_VAL(val) ((val) >> 32)
^^^^^^^^^^^^
Some stray tabs here and above, pls pay attention to vertical alignment too.
> +
> +/* Page State Change NAE event */
> +#define SNP_PAGE_STATE_CHANGE_MAX_ENTRY 253
> +struct __packed snp_page_state_header {
> + uint16_t cur_entry;
> + uint16_t end_entry;
> + uint32_t reserved;
> +};
> +
> +struct __packed snp_page_state_entry {
> + uint64_t cur_page:12;
> + uint64_t gfn:40;
> + uint64_t operation:4;
> + uint64_t pagesize:1;
> + uint64_t reserved:7;
> +};
Any particular reason for the uint<width>_t types or can you use our
shorter u<width> types?
> +
> +struct __packed snp_page_state_change {
> + struct snp_page_state_header header;
> + struct snp_page_state_entry entry[SNP_PAGE_STATE_CHANGE_MAX_ENTRY];
Also, looking further into the patchset, I wonder if it would make sense
to do:
s/PAGE_STATE_CHANGE/PSC/g
to avoid breaking lines of huge statements:
+ if ((GHCB_SEV_GHCB_RESP_CODE(val) != GHCB_SNP_PAGE_STATE_CHANGE_RESP) ||
+ (GHCB_SNP_PAGE_STATE_RESP_VAL(val) != 0))
+ sev_es_terminate(GHCB_SEV_ES_REASON_GENERAL_REQUEST);
and turn them into something more readable
+ if ((GHCB_SEV_GHCB_RESP_CODE(val) != GHCB_SNP_PSC_RESP) ||
+ (GHCB_SNP_PSC_RESP_VAL(val)))
+ sev_es_terminate(GHCB_SEV_ES_REASON_GENERAL_REQUEST);
Also, you have GHCB_SEV and GHCB_SNP prefixes and I wonder whether we
even need them and have everything be prefixed simply GHCB_ because that
is the protocol, after all.
Which will then turn the above into:
+ if ((GHCB_RESP_CODE(val) != GHCB_PSC_RESP) || (GHCB_PSC_RESP_VAL(val)))
+ sev_es_terminate(GHCB_REASON_GENERAL_REQUEST);
Oh yeah baby! :-)
Thx.
--
Regards/Gruss,
Boris.
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