Re: [PATCH v3 2/4] x86/sev: Change snp_guest_issue_request's fw_err

[Tom Lendacky <thomas.lendacky@amd.com>]

On 10/21/22 11:59, Dionna Glaze wrote:
> The GHCB specification declares that the firmware error value for a
> guest request will be stored in the lower 32 bits of EXIT_INFO_2.
> The upper 32 bits are for the VMM's own error code. The fw_err argument
> is thus a misnomer, and callers will need access to all 64 bits.
> 
> The type of unsigned long also causes problems, since sw_exit_info2 is
> u64 (unsigned long long) vs the argument's previous unsigned long*.
> The signature change requires the follow-up change to
> drivers/virt/coco/sev-guest to use the new expected type in order to
> compile.
> 
> The firmware might not even be called, so we bookend the call with the
> no firmware call error and clearing the error.
> 
> Cc: Tom Lendacky <Thomas.Lendacky@amd.com>
> Cc: Paolo Bonzini <pbonzini@redhat.com>
> Cc: Joerg Roedel <jroedel@suse.de>
> Cc: Peter Gonda <pgonda@google.com>
> Cc: Thomas Gleixner <tglx@linutronix.de>
> Cc: Dave Hansen <dave.hansen@linux.intel.com>
> 
> Fixes: d5af44dde546 ("x86/sev: Provide support for SNP guest request NAEs")
> Signed-off-by: Dionna Glaze <dionnaglaze@google.com>
> ---
>   arch/x86/include/asm/sev.h |  4 ++--
>   arch/x86/kernel/sev.c      | 11 ++++++++---
>   2 files changed, 10 insertions(+), 5 deletions(-)
> 
> diff --git a/arch/x86/include/asm/sev.h b/arch/x86/include/asm/sev.h
> index ebc271bb6d8e..8ebd78b6a57c 100644
> --- a/arch/x86/include/asm/sev.h
> +++ b/arch/x86/include/asm/sev.h
> @@ -196,7 +196,7 @@ void snp_set_memory_private(unsigned long vaddr, unsigned int npages);
>   void snp_set_wakeup_secondary_cpu(void);
>   bool snp_init(struct boot_params *bp);
>   void __init __noreturn snp_abort(void);
> -int snp_issue_guest_request(u64 exit_code, struct snp_req_data *input, unsigned long *fw_err);
> +int snp_issue_guest_request(u64 exit_code, struct snp_req_data *input, u64 *exitinfo2);
>   #else
>   static inline void sev_es_ist_enter(struct pt_regs *regs) { }
>   static inline void sev_es_ist_exit(void) { }
> @@ -217,7 +217,7 @@ static inline void snp_set_wakeup_secondary_cpu(void) { }
>   static inline bool snp_init(struct boot_params *bp) { return false; }
>   static inline void snp_abort(void) { }
>   static inline int snp_issue_guest_request(u64 exit_code, struct snp_req_data *input,
> -					  unsigned long *fw_err)
> +					  unsigned long *exitinfo2)


s/unsigned long/u64/

>   {
>   	return -ENOTTY;
>   }
> diff --git a/arch/x86/kernel/sev.c b/arch/x86/kernel/sev.c
> index a428c62330d3..5a402df7549e 100644
> --- a/arch/x86/kernel/sev.c
> +++ b/arch/x86/kernel/sev.c
> @@ -22,6 +22,7 @@
>   #include <linux/efi.h>
>   #include <linux/platform_device.h>
>   #include <linux/io.h>
> +#include <linux/psp-sev.h>
>   
>   #include <asm/cpu_entry_area.h>
>   #include <asm/stacktrace.h>
> @@ -2175,7 +2176,7 @@ static int __init init_sev_config(char *str)
>   }
>   __setup("sev=", init_sev_config);
>   
> -int snp_issue_guest_request(u64 exit_code, struct snp_req_data *input, unsigned long *fw_err)
> +int snp_issue_guest_request(u64 exit_code, struct snp_req_data *input, u64 *exitinfo2)
>   {
>   	struct ghcb_state state;
>   	struct es_em_ctxt ctxt;
> @@ -2186,9 +2187,11 @@ int snp_issue_guest_request(u64 exit_code, struct snp_req_data *input, unsigned
>   	if (!cc_platform_has(CC_ATTR_GUEST_SEV_SNP))
>   		return -ENODEV;
>   
> -	if (!fw_err)
> +	if (!exitinfo2)
>   		return -EINVAL;
>   
> +	*exitinfo2 = SEV_RET_NO_FW_CALL;
> +
>   	/*
>   	 * __sev_get_ghcb() needs to run with IRQs disabled because it is using
>   	 * a per-CPU GHCB.
> @@ -2218,9 +2221,11 @@ int snp_issue_guest_request(u64 exit_code, struct snp_req_data *input, unsigned
>   		    ghcb->save.sw_exit_info_2 == SNP_GUEST_REQ_INVALID_LEN)
>   			input->data_npages = ghcb_get_rbx(ghcb);
>   
> -		*fw_err = ghcb->save.sw_exit_info_2;
> +		*exitinfo2 = ghcb->save.sw_exit_info_2;

Looks like you can do "*exitinfo2 = ghcb->save.sw_exit_info_2;" just 
before the "if (ghcb->save.sw_exit_info_2) {". That would eliminate the 
need to assign it in each branch of the if.

Thanks,
Tom

>   
>   		ret = -EIO;
> +	} else {
> +		*exitinfo2 = 0;
>   	}
>   
>   e_put: